Effect of injection molding parameters on properties of cross-linked low-density polyethylene/ethylene vinyl acetate/organoclay nanocomposite foams

Injection molding of foam articles has always attracted much interest because of elimination of sink mark, good dimensional stability and reduced production cost. In this study, the nanocomposite samples based on low-density polyethylene/ethylene vinyl acetate/organo montmorillonite were processed into foams by injection molding method. Nanocomposites were prepared by co-rotating a twin-screw extruder. The experimental design was based on Box?CBehnken method and parameters such as injection rate, mold temperature and nanolayered silica content were examined in relation to physico-mechanical properties of foams using response surface methodology. Three levels of injection rate (30, 60 and 90?mm/s), nanoclay content (0, 3 and 6?phr) and mold temperature (160, 175 and 190?°C) were chosen. The mathematical model and response surface graphs were employed to illustrate the relationship between the variable parameters and foam properties. The results revealed that the cell size and cell density as the main characteristics of the foams were affected by all parameters. Cell density of samples was affected by mold temperature, injection rate and nanoclay content. At high level of nanocontent the increase of injection rate was accompanied by decreases in density. Tensile strength and specific compression modulus of samples passed through a maximum versus mold temperature due to competition between cross-linking reaction and cell growth. At high mold temperature and injection rate, the cell rupture occurred because of low viscosity of the compounds at these conditions.     

A simple method for preparation of polymer microcellular foams by in situ generation of supercritical carbon dioxide from dry ice

In this work, poly(methyl methacrylate) (PMMA) and PMMA/nanoclay nanocomposite microcellular foams were successfully prepared using a simple method based on in situ generation of supercritical carbon dioxide (CO₂) from dry ice. The method was compared with conventional methods exempted from high pressure pump and a separate CO₂ tank. Effect of various processing conditions such as saturation temperature and pressure and clay concentration on cellular morphology and hardness of the prepared microcellular foams was examined. State of the clay dispersion in the prepared PMMA/clay nanocomposites was characterized using X-ray diffraction and transmission electron microscopy techniques. Field emission scanning electron microscopy was used to study cellular morphology of the prepared foams. It was observed that elevation of saturation temperature from 85 to 105 °C at constant saturation pressure increased cell density and decreased average cell size of the prepared PMMA foams. Furthermore, an increase in saturation pressure from 120 to 180 bar resulted in a reduction in average cell diameter and an increase in cell density of the prepared PMMA foams. On the basis of the gathered results, optimum conditions for preparation of PMMA microcellular foams were determined and applied for preparation of PMMA/nanoclay microcellular foams. It was shown that incorporation of clay into the polymer matrix resulted in a finer and more uniform cellular morphology in the final microcellular foams. It was also observed that incorporation of nanoclay into the prepared foams, up to 3 wt%, led to a moderate increase in the foam hardness.     

Cure Characteristics and Mechanical Properties of Natural Rubber–Layered Clay Nanocomposites

The effect of interlayer distance of nanoclay on mechanical properties, cure characteristics, and swelling resistance of natural rubber (NR) in varying clay proportion were studied. X-ray diffraction results of nanocomposite with 10 phr of nanoclay showed the formation of an intercalated structure. The rate of vulcanization and maximum torque value of the nanocomposite are higher than the gum compound. Nanocomposites with clay having higher interlayer distance shows superior mechanical properties. Mechanical properties gradually increase with increase in clay loading up to 10 phr. A 50% increase in tensile strength and about 150% increase in modulus at 300% elongation were observed for the nanocomposite with 10 phr clay loading. Better barrier properties offered by the nanocomposites due to the presence of tortous path was confirmed by the Nielson's model.     

Mechanical, thermal and transport properties of nitrile rubber (NBR)—nanoclay composites

The article describes the properties of nitrile rubber (NBR)??nanoclay composites prepared by a two-step method. viz. preparation of a 3:1 [by weight] masterbatch of NBR and nanoclay followed by compounding on a two roll mill and molding at 150?°C and 20?MPa pressure. The tensile strength, elongation at break, modulus, storage modulus (E??) and loss modulus (E??) increased with the nanofiller content, reached the maximum value at 5 phr and decreased thereafter. The solvent uptake, diffusion, sorption and permeation constants decreased with nanoclay content with the minimum value at 5 phr nanoclay. The mechanism of solvent diffusion through the nanocomposites was found to be Fickian. Thermodynamic constants such as enthalpy and activation energy were also evaluated. The dependence of various properties on nanoclay content was correlated to the morphology of the nanocomposites. supported by morphological analysis.     

Mechanical, thermal and transport properties of nitrile rubber (NBR)—nanoclay composites

The article describes the properties of nitrile rubber (NBR)—nanoclay composites prepared by a two-step method. viz. preparation of a 3:1 [by weight] masterbatch of NBR and nanoclay followed by compounding on a two roll mill and molding at 150 °C and 20 MPa pressure. The tensile strength, elongation at break, modulus, storage modulus (E’) and loss modulus (E”) increased with the nanofiller content, reached the maximum value at 5 phr and decreased thereafter. The solvent uptake, diffusion, sorption and permeation constants decreased with nanoclay content with the minimum value at 5 phr nanoclay. The mechanism of solvent diffusion through the nanocomposites was found to be Fickian. Thermodynamic constants such as enthalpy and activation energy were also evaluated. The dependence of various properties on nanoclay content was correlated to the morphology of the nanocomposites. supported by morphological analysis.     

Effect of processing parameters on morphology and tensile properties of PP/EPDM/organoclay nanocomposites fabricated by friction stir processing

Nanocomposites-based on polypropylene (PP), ethylene-propylene diene monomer (EPDM) and Cloisite 15A have wide applications in automotive and aerospace industries and medical apparatus due to their excellent mechanical, thermal and chemical properties. In this study, a nanocomposite of PP/EPDM/nanoclay containing PP (77 wt%), EPDM (20 wt%) and nanoclay (3 wt%) was fabricated by friction stir processing (FSP) method. X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry and tensile testing were performed to determine the morphology and tensile properties of this nanocomposite. The Box-Behnken design was applied to investigate the effect of the process parameters such as tool rotational speed, traverse speed and shoulder temperature on the tensile properties of the nanocomposite. The results showed that the tensile strength increased from 15.8 to 18.2 MPa with increasing the tool rotational speed and shoulder temperature while the elongation-at-break dropped from 46 to 22 %. A maximum tensile strength of 17.6 MPa and a minimum elongation-at-break of 26 % were obtained at the traverse speed of 40 mm/min when the rotational speed and shoulder temperature were at the central levels themselves. The prediction models showed that when the tool rotational speed, traverse speed and shoulder temperature were set, in the given order, as 1200 rpm, 45.65 mm/min and 113.65 °C, a simultaneous maximization of tensile strength of 16.03 MPa and elongation-at-break of 46.41 % was obtained.     

Synthesis of β-myrcene-based macroporous nanocomposite foams: Altering the morphological and mechanical properties by using organo-modified nanoclay

Organo-modified nanoclay incorporated high internal phase emulsions (HIPEs) were successfully used for the preparation of macroporous nanocomposite foams. Due to the aim of obtaining mechanically improved foams, HIPEs were prepared by using a monomer mixture composed of β-myrcene and ethylene glycol dimethacrylate. Accordingly, two groups of macroporous nanocomposite foams were synthesized depending on the nanoclay type. The morphological analysis demonstrated that the pore openness of the resulting nanocomposites were significantly improved due to the decrease in the average cavity size and increase in the interconnected pore size. In terms of mechanical properties, it was found that filling 1 wt% of nanoclay which is surface modified by hydrogenated tallow lead to a 33% of increment in the compression modulus, as compared to the neat foam. However, loading 5 wt% of nanoclay having octadecylamine and aminopropyltriethoxysilane surface groups caused only 11% of increment in the compression modulus, as compared to the neat foam.     

Effects of parameter changes on the structure and properties of low‐density polyethylene foam

Several parameters, such as crosslinking agent concentration, blowing agent concentration, and temperature, were varied to evaluate their effects on the structure and mechanical properties of low‐density polyethylene (LDPE) foams. Dicumyl peroxide (DCP) was used as crosslinking agent, while azodicarbonamide (ADC) was utilized as the blowing agent at different levels. The formulations were prepared by using a thermostatically controlled heated two‐roll mill and foamed by using a compression molding technique via a single‐stage foaming process at three foaming temperatures (165, 175, and 185°C). The resultant LDPE foams were characterized and found to have a closed cell structure. The density and gel content increased proportionally with crosslinking level, whereas density decreased when ADC level and foaming temperature were increased. Another characteristic evaluated was the foam cell size decreased when the crosslinking level and foaming temperature were increased. In contrast, increasing the ADC concentration only gave a maximum cell size increase up to 6 phr that decreased when 8 phr of ADC was used. Results also indicated that compression stress increased proportionally with DCP level and decreased when ADC concentration and foaming temperature were increased. Impact studies on the prepared foams showed that their ability to absorb impact energy decreased with increasing crosslinking level, foaming temperature, and blowing agent concentration. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Ethylene vinyl acetate copolymer (EVA)/multiwalled carbon nanotube (MWCNT) nanocomposite foams

In this study, multiwalled carbon nanotube (MWCNT) and ethylene vinyl acetate copolymer (EVA) nanocomposite bulk foams were prepared for static dissipative applications by using melt compounding method, the most compatible with current industrial applications. Closed‐cell structure was verified with Scanning Electron Microscope. All the mechanical properties investigated improved with increasing content of MWCNT except elongation at break. At 5 phr of MWCNT, significant improvement of mechanical properties and compression set were observed. Also, the surface resistivity begins to decrease at 5 phr of MWCNT. Interestingly, the increase of surface resistivity of nanocomposite foams with 8 and 10 phr MWCNT were observed with increasing thickness of removed surface layers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Modified preparation of HDPE/clay nanocomposite by in situ polymerization using a metallocene catalyst

In this study, preparation of high-density polyethylene (HDPE)/clay nanocomposite by in situ polymerization of ethylene using a zirconocene catalyst (bis-(cyclopentadienyl) zirconium dichloride (Cp₂ZrCl₂)) was investigated. To obtain higher efficiency, nanoclay particles (Na-montmorillonite) were modified by ammonia (NH₃), NH₃/methylaluminoxane (MAO), NH₃/dodecylamine (DDA), and NH₃/MAO/DDA systems. The results showed that the activity of the catalyst supported on the nanoclay particles modified by NH₃/MAO (762 g_p/mmol (Zr) t [atm]) was higher than that of the one supported on the unmodified nanoclay as well as the other prepared modified nanoclay-supported catalyst systems. The catalyst activities versus MAO concentration in NH₃/MAO treatment system and versus DDA concentration in NH₃/DDA system showed a maximum. Unexpectedly, a very low catalyst activity (180 g_p/mmol(Zr) t [atm]) was obtained using NH₃/MAO/DDA system. X-ray diffraction patterns showed that the HDPE/clay nanocomposites prepared by NH₃/MAO/DDA treatment system had less intercalated structure. Fourier transform infrared (FTIR) spectroscopy confirmed that water molecules of the nanoclay particles were reduced by NH₃ modification. DSC results revealed that crystallinity of the HDPE/clay nanocomposites increased with the modification of the nanoclay particles. The maximum degree of crystallinity of 80.8% was obtained for HDPE/clay nanocomposites prepared by the nanoclay modified by NH₃. In addition, nanoclay modification with NH₃, NH₃/MAO, and NH₃/DDA systems resulted in higher thermal decomposition temperature (~30 °C higher than 480 °C of the unmodified one). Such increase was not observed for the NH₃/MAO/DDA treatment system. Dynamic mechanical analysis showed an increase in the elastic modulus of the nanocomposite samples prepared by modified nanoclay particles, as well. Meanwhile, modification of the nanoclay particles by NH₃ led to the highest elastic behavior compared to the other modification systems. It was about 4.6 GPa which was 28% higher than the elastic modulus of the nanocomposite prepared by unmodified nanoclay particles.     

Efficacy of Novel Nanoclay in Autohesive Tack of Brominated Isobutylene-co-p-Methylstyrene (BIMS) Rubber

Autohesive tack is the ability of two unvulcanized rubber surfaces to resist separation after they are brought into contact for a short period under light pressure. In this work, the effect of unmodified montmorillonite (MMT) nanoclay on autohesive tack of brominated isobutylene-co-p-methylstyrene (BIMS) rubber was investigated by a 180° peel test. The nanocomposites were characterized using X-ray diffraction (XRD) and atomic force microscopy (AFM). The autohesive tack strength dramatically increased with nanoclay concentration up to 8 phr, beyond which it reached apparently a plateau at 16 phr of nanoclay concentration. The tack strength of 16 phr of nanoclay loaded sample was nearly 158% higher than the tack strength of neat BIMS rubber. Various tack governing factors such as green strength, creep compliance, entanglement molecular weight, relaxation time, self-diffusion coefficient, and monomer friction coefficient were analyzed. The addition of nanoclay reduced the extent of molecular diffusion at the tack junction by reducing the chain mobility; however, the diffusion was still sufficient to achieve bond formation. Furthermore, the less diffused chains of the nanocomposite samples showed greater bond breaking resistance due to an increase in cohesive strength, onset of transition zone relaxation time, and monomer friction coefficient value of the BIMS matrix owing to the nanoclay reinforcement. On the other hand, the more diffused chains of the unfilled sample exhibited facile chain separation due to the poor cohesive strength of the BIMS matrix.     

Preparation and characterization of poly(ε‐caprolactone)/calcium carbonate nanocomposites and nanocomposite foams

Biodegradable poly(ε‐caprolactone) (PCL)/calcium carbonate (CaCO₃) nanocomposites were prepared and characterized. Effect of CaCO₃ on thermal and mechanical properties of PCL matrix was studied. Results showed that CaCO₃ acts as a crystallization nucleating agent and introduction of CaCO₃ leads to improved mechanical properties of the PCL matrix. PCL/CaCO₃ nanocomposite foams were prepared using chemical foaming method. Cellular parameters such as mean cell size, cell wall thickness, and cell density were collected. The cellular structure of nanocomposite foams changes with different CaCO₃ loading. Mean cell size achieved the minimum value at 5 wt% CaCO₃ loading, and cell wall thickness increased with CaCO₃ content. The changes in cellular structure and improvement of mechanical properties also enhanced the mechanical properties of PCL/CaCO₃ nanocomposite foams. Compressive moduli of PCL/CaCO₃ nanocomposite foams with similar density increased with increasing CaCO₃ loading. POLYM. COMPOS., 31:1653–1661, 2010. © 2009 Society of Plastics Engineers     

Morphology and interaction of nanocomposite foams formed with organo-palygorskite and ethylene-vinyl acetate copolymers

To obtain excellent mechanical properties of polymer nanocomposite foams without sacrificing the lower density through popular and friendly means. Organically modified palygorskite (OPal) was prepared with γ-aminopropyltriethoxysilane on the surface of rod-shaped Pal particles, and nanocomposite foams based on ethylene-vinyl acetate (EVA) copolymer was prepared by melt-blending EVA with OPal. Fourier transform infrared spectroscopy (FTIR) was used to investigate the interaction between OPal and EVA matrix, and the OPal/EVA nanocomposites were also characterized by X-ray photoelectron spectra (XPS), X-ray diffraction analysis (XRD) and differential scanning calorimetry (DSC). The dispersivity of OPal in the EVA matrix and the morphology of the foams were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and the OPal/EVA nanocomposite foams were also characterized by thermogravimetric analysis (TGA). The effect of OPal content in the foam samples on the cellular structure and mechanical properties was investigated. Our studies indicate that the OPal nanofibers could be used as a heterogeneous nucleation agent to reduce the average cell diameter. The uniformity of cell structure of the foams was improved, and the physical properties of OPal/EVA nanocomposite foams were enhanced by the addition of OPal. The density of OPal/EVA nanocomposite foams was decreased to 0.133 g/cm³. Also, the best tear strength, peel strength and compression set values of nanocomposite foams were 4.65, 2.65 N/mm and 25.5 %, which were improved by 36.0, 54.3 and 12.0 %, respectively, compared with those of the initial foam.     

Batch foaming of SAN/clay nanocomposites with scCO2: A very tunable way of controlling the cellular morphology

This paper aims at elucidating some important parameters affecting the cellular morphology of poly(styrene-co-acrylonitrile) (SAN)/clay nanocomposite foams prepared with the supercritical CO₂ technology. Prior to foaming experiments, the SAN/CO₂ system has first been studied. The effect of nanoclay on CO₂ sorption/desorption rate into/from SAN is assessed with a gravimetric method. Ideal saturation conditions are then deduced in view of the foaming process. Nanocomposites foaming has first been performed with the one-step foaming process, also called depressurization foaming. Foams with different cellular morphology have been obtained depending on nanoclay dispersion level and foaming conditions. While foaming at low temperature (40 °C) leads to foams with the highest cell density (∼10¹²-10¹⁴ cells/cm³), the foam expansion is restricted (d∼0.7-0.8 g/cm³). This drawback has been overcome with the use of the two-step foaming process, also called solid-state foaming, where foam expansion occurs during sample dipping in a hot oil bath (d∼0.1-0.5 g/cm³). Different foaming parameters have been varied, and some schemes have been drawn to summarize the characteristics of the foams prepared - cell size, cell density, foam density - depending on both the foaming conditions and nanoclay addition. This result thus illustrates the huge flexibility of the supercritical CO₂ batch foaming process for tuning the foam cellular morphology.     

Study on the phase behavior of a toughened epoxy adhesive and its bond-strength properties at liquid nitrogen temperature

The phase behavior of an epoxy adhesive toughened with a polyether was investigated. The adhesive, cured at 60^°C, formed a separated island-phase structure with diameters of 0.4– 0.8 μ m, 3–5 μ m and 80–100 μ m at toughener contents of 10 phr, 20 phr and 30 phr, respectively. Phase inversion occurred at a toughener content of 40 phr. The bound-strength properties of the toughened adhesive were highly influenced by this phase behavior. The measured lap-shear strengths on aluminum at ?196^°C, 25^°C, 140^°C and peel strength at 25^°C for the adhesive containing 20 phr toughener and 75 phr aluminum powder were 26.5 MPa, 24.2 MPa, 11.0 MPa and 2.2 kN/m, respectively. This showed that the epoxy adhesive studied could be used in a wide temperature range of ?196^°C – 140^°C with good bound-strength properties.     

Extrusion of polystyrene nanocomposite foams with supercritical CO2

Intercalated and exfoliated polystyrene/nano‐clay composites were prepared by mechanical blending and in situ polymerization respectively. The composites were then foamed by using CO₂ as the foaming agent in an extrusion foaming process. The resulting foam structure is compared with that of pure polystyrene and polystyrene/talc composite. At a screw rotation speed of 10 rpm and a die temperature of 200°C, the addition of a small amount (i.e., 5 wt%) of intercalated nano‐clay greatly reduces cell size from 25.3 to 11.1 μm and increases cell density from 2.7 × 10⁷ to 2.8 × 10⁸ cells/cm³. Once exfoliated, the nanocomposite exhibits the highest cell density (1.5 × 10⁹ cells/cm³) and smallest cell size (4.9 μm) at the same particle concentration. Compared with polystyrene foams, the nanocomposite foams exhibit higher tensile modulus, improved fire retardance, and better barrier property. Combining nanocomposites and the extrusion foaming process provides a new technique for the design and control of cell structure in microcellular foams.     

Performance evaluation of polymer/clay nanocomposite thermal protection systems based on polyethylene glycol phase change material

Phase change materials (PCMs) are substances with a high heat of fusion which, through melting and solidifying at specified temperatures, are capable of storing or releasing a large amount of thermal energy. This phenomenon can be utilized in designing the heat protective materials as well as in the thermal energy storage systems. In this work, effects of polyethylene glycol (PEG) as PCM and montmorillonite nanoclay, as a thermal property modifier in epoxy resin on the thermal protection performance of nanocomposites were studied. A special performance evaluation test was designed to study the top surface temperature behavior of prepared samples under back surface heating. Results indicated that increasing PCM content improved thermal protection performance, but lower thermal diffusivity was found for the sample containing 60 wt% of PEG, with a 31 % decrease in top surface temperature. These results show that increasing of top surface temperature of samples containing PCM was very slow when compared with the neat epoxy sample. A top surface temperature behavior of these samples shows a plateau in melting region of PCM which makes a delay time in temperature increment compared with that of the neat epoxy sample. Moreover, heat protection performances of low filled nanocomposite blends, i.e., nanocomposite blends with 5 and 7 wt% of clay in PEG have been improved about 10 % in comparison with EP/PEG60 blend.     

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. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Mechanical and Damping Properties of Glass Fiber and Mica-Reinforced Epoxy Composites

Mica/glass fiber-reinforced epoxy with 0° and 45° ply angle were prepared by hand lay-up and the mechanical and damping properties were studied. Results show that the addition of mica resulted in decrease of tensile strength and modulus for both composites. Althogh flexural strength and modulus of composites with 45° appeared a maximum at 5 phr mica loading, that of composites with 0° reached a maximum at 10 phr mica loading. For composites with 0°, damping ratio reaches maximum at 5 phr mica. Although for composites with 45°, damping ratio decrease with increasing mica loading.     

Effect of Acidic and Basic Solutions on Electron Beam Irradiated Epoxy Nanocomposites Containing Nanoclay,CaCO3 and TiO2 Nanoparticles

High chemical resistance is the main prerequisites for materials that are intended to be utilized in usages such as chemicals storage containers production. Nanocomposites of epoxy resin containing nanoclay, CaCO₃ and TiO₂ nanoparticles were prepared and their chemical resistance was studied. Moreover, the effect of electron beam irradiation was explored. TEM micrographs proved the dispersion of nano-size particles in the polymeric matrix. XRD patterns showed an exfoliated structure for nanocomposite containing 1 % nanoclay and intercalated structures for nanocomposites with higher nanoclay contents. SEM showed the pits that appeared in epoxy/nanoclay structure due to chemical corrosion. Weight loss measurements revealed that an addition of 1 % nanoclay to the epoxy matrix is effective for improving the chemical properties of the polymer. Desirable effect of 100 kGy irradiation on chemical resistance properties of the samples was also observed in both acidic and basic environments.