Effect of screw rotation speed on the properties of polystyrene/organoclay nanocomposites prepared by a twin‐screw extruder

We discuss the effect of screw rotation speed on the mechanical and rheological properties and clay dispersion state of polystyrene (PS)/organoclay (clay) nanocomposites prepared by melt compounding with a counterrotating‐type twin‐screw extruder. Poly(styrene‐co‐vinyloxazolin) (OPS) was used as an additional material. The Young's modulus of the PS/OPS/clay nanocomposites showed the maximum value at a screw rotation speed of 70 rpm in this study. This implied the existence of an optimized screw rotation speed for the melt compounding of the polymer/clay nanocomposites. For PS/clay systems without the addition of OPS, the peak intensity from clay increased and the distance between clay platelets in the nanocomposites decreased with the screw rotation speed. On the other hand, inverse results were obtained for PS/OPS/clay systems. According to the transmission electron microscopy photographs, the PS/OPS/clay nanocomposite at 70 and 100 rpm had fully exfoliated clay platelets. The dynamic rheological properties of the PS/clay nanocomposites were almost the same as those of neat PS. On the other hand, the storage and loss moduli of the PS/OPS/clay nanocomposites at the same frequency were larger than those of the PS/clay system. On the whole, the bonding between clay platelets and PS was important for increasing the viscosity and elasticity in the melts of the PS/clay system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1165–1173, 2006     

EVA‐Montmorillonite Nanocomposites: Effect of Processing Conditions

Summary: The aim of this study is to examine the effect of the compounding apparatus and of processing conditions on the properties of an organoclay‐poly[ethylene‐co‐(vinyl acetate)] (EVA) nanocomposite. The filled materials were prepared using either a discontinuous batch mixer, a single screw extruder, a counter rotating intermeshing twin‐screw compounder or a corotating intermeshing twin‐screw extruder. The characterization of the obtained nanocomposites was performed by XRD, thermogravimetry, mechanical and rheological measurements. The study has shown the possibility of producing nanocomposites based on EVA and a commercial organoclay (Cloisite 15A) by several mixing equipments. In fact all the prepared composite materials exhibit a larger interlayer clay spacing in comparison with the pristine organoclay. Moreover their elastic modulus is significantly increased from 50 to 100% depending on the processing conditions.

X‐ray diffraction of the master (Sample A) and the clay used for its preparation (Cloisite 15A).     

Natural rubber/poly(ethylene‐co‐vinyl acetate)‐blend‐based nanocomposites

Natural rubber (NR)/poly(ethylene‐co‐vinyl acetate) (EVA) blend–clay nanocomposites were prepared and characterized. The blend nanocomposites were prepared through the melt mixing of NR/EVA in a ratio of 40/60 with various amounts of organoclay with an internal mixer followed by compression molding. X‐ray diffraction patterns revealed that the nanocomposites formed were intercalated. The formation of the intercalated nanocomposites was also indicated by transmission electron microscopy. Scanning electron microscopy, used to study the fractured surface morphology, showed that the distribution of the organoclay in the polymer matrix was homogeneous. The tensile modulus of the nanocomposites increased with an increase in the organoclay content. However, an increase in the organoclay content up to 5 phr did not affect the tensile strength, but the organoclay reduced this property when it was increased further. This study also indicated that a low silicate content dispersed in the blend matrix was capable of increasing the storage modulus of the material. The addition of the organoclay also increased the decomposition temperature of the NR/EVA blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 353–362, 2006     

Enhancement of radiation‐resistant effect in ethylene–vinyl acetate copolymers by the formation of ethylene–vinyl acetate copolymers/clay nanocomposites

Ethylene–vinyl acetate (EVA) copolymers/clay nanocomposites, prepared by using nonreactive organophilic clay and reactive organophilic clay, were characterized by X‐ray diffraction and by high‐resolution transmission electron microscopy. The influence of gamma irradiation on the structure and properties of the pure EVA and EVA/clay nanocomposites was systematically investigated. In the presence of gamma radiation, the clay can effectively restrain the increase of the storage modulus of EVA/clay nanocomposites, which was supported by dynamical mechanical analysis. Gamma irradiation had almost no effect on the thermal properties of EVA/clay nanocomposites by using nonreactive organophilic clay, but it obviously improved the thermal stability of EVA/clay nanocomposites by using reactive organophilic clay. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2532–2538, 2005     

Rheological properties of poly(acrylonitrile‐co‐methyl acrylate)/clay nanocomposites prepared via emulsion polymerization

Poly(acrylonitrile‐co‐methyl acrylate)/clay nanocomposites were prepared by free radical polymerization in emulsion using 2‐acrylamido‐2‐methyl‐1‐propanesulphonic acid (AMPS) as a compatibilizer. The resultant nanocomposites were of partially exfoliated morphology despite the variations in clay content among the nanocomposites, as confirmed by transmission electron microscopy and small‐angle X‐ray scattering analysis. Rheological studies of these materials were carried out using parallel plate geometry. The storage modulus increased monotonically with increasing clay content throughout the frequency range studied. However, the neat copolymer, poly(acrylonitrile‐co‐methyl acrylate) and its nanocomposites, exhibited long relaxation behavior as the storage modulus (G′) was greater than the loss modulus (G″) throughout the angular frequency range studied. The complex viscosity of the nanocomposites increased with increasing clay content and they exhibited shear‐thinning behavior. Despite the enhanced rheological properties observed, the copolymer and its nanocomposites underwent structural changes during oscillatory measurements due to cyclization reactions. POLYM. COMPOS., 32:59–66, 2011. © 2010 Society of Plastics Engineers     

Morphology, rheology and dynamic mechanical properties of PP/EVA/clay nanocomposites

This paper reports on morphology, rheology and dynamic mechanical properties of polypropylene (PP)/ethylene vinyl acetate (EVA) copolymer/clay nanocomposite system prepared via a single step melt compounding process using a twin screw micro-compounder. Scanning electron microscopic (SEM) investigations revealed that the dispersed phase droplet size was reduced with incorporation of an organo-modified montmorillonite (OMMT). This reduction was more significant in presence of a maleated PP (PP-g-MAH) used as compatibilizer. Phase inversion in the compatibilized blends caused a further decrease in PP droplet size. The OMMT gallery spacing was higher in nanocomposites with EVA as matrix which could be attributed to higher tendency of OMMT nanoparticles towards EVA rather than PP. This enhanced tendency was confirmed by rheological analysis too. Transmission electron microscopy (TEM) results also showed that the majority of OMMT nanoparticles were localized on the interface and within EVA droplets. According to dynamic mechanical analysis, the compatibilized nanocomposites showed higher storage and loss moduli due to better dispersion of OMMT layers. The modulus enhancement of nanocomposites as a function of OMMT volume fraction was modeled by Halpin-Tsai’s-Nielsen expression of modulus for nanocomposites. The results of modeling suggested that the aspect ratio of the intercalated OMMT, in the form of Einstein coefficient (K _E), plays a determining role in the modulus enhancement of nanocomposites.     

An investigation on the correlation between rheology and morphology of nanocomposite foams based on low‐density polyethylene and ethylene vinyl acetate blends

This article presents the correlation between rheology and morphology of nanocomposite foams of low‐density polyethylene (LDPE), ethylene vinyl acetate (EVA), and their blends. LDPE/EVA nanocomposites were prepared via melt mixing and then foamed using batch foaming method. To assess the rheological behavior of polymer melts, frequency sweep and creep recovery tests were done. Morphology of the samples was also studied by scanning electron microscopy and X‐ray diffraction. The results showed that with increase in clay content, storage modulus, complex and zero shear viscosities will be increased, which affect the foam morphology. In addition, elasticity plays an important role in foaming process, in a way that samples with more elasticity percentage have the highest cell density and the lowest cell size. POLYM. COMPOS., 31:1808–1816, 2010. © 2010 Society of Plastics Engineers.     

Evaluation of different amine‐functionalized polyethylenes as compatibilizers for polyethylene film nanocomposites

The compatibilization effects provided by different amine‐functionalized polyethylenes (PEs) versus those provided by a maleated polyethylene (PEgMA), for forming PE‐based film nanocomposites, were studied. Amine‐functionalized PEs were prepared by reaction of PEgMA with two primary amines, 2‐aminoethanol (EA) and 1,12‐aminododecane (D12), and a tertiary amine, 2‐[2‐(dimethylamino)ethoxy]ethanol (DMAE), in the melt to form the corresponding PEgEA, PEgD12 and PEgDMAE. Nanocomposites were prepared by melt mixing in a twin‐screw extruder PE and these three functionalized compatibilizers with a modified montmorillonite clay. The purpose of the current work was to determine the effect of the various amine‐functionalized PEs on the degree of exfoliation and optical properties of PE–clay nanocomposites in order to obtain nanocomposite films for greenhouse cover applications. Fourier transform infrared analysis confirmed the formation of the amine‐modified PE compatibilizers. Structural, morphological, mechanical, rheological and optical properties of film samples were used to characterize the nanocomposites. All the amine‐modified PE‐compatibilized nanocomposites had better clay exfoliation compared to uncompatibilized PE composites. Results showed that PEgDMAE formed highly exfoliated morphology and a favorable balance between mechanical (stiffness and ductility), optical and thermal insulating film properties even at higher clay contents. It was determined that nanocomposites with greater exfoliated structure showed better optical and thermal insulating film properties. PEgEA and PEgD12 compatibilizers did not provide a better interaction for exfoliation of the organoclay than the PEgMA material. The PEgDMAE compatibilizer led to a highly exfoliated morphology and a favorable balance between mechanical, optical and thermal insulating film properties even at higher clay contents. The PEgDMAE film nanocomposites could be used ideally for greenhouse cover applications. Copyright © 2010 Society of Chemical Industry     

Morphology and chain mobility of reactive blend nanocomposites of PP‐EVA/Clay

Polypropylene (PP)‐ethylene vinyl acetate (EVA)/clay nanocomposites were prepared via reactive blending using dicumyl peroxide (DCP) as an initiator with the goal of enhancing the interaction between both phases and modified nanoclay. The effect of the reactive blending and clay incorporation strategies (direct and masterbatch) on the blend and nanostructure morphology, and chain mobility of nanocomposites were studied. The chemical analysis showed the chemical bonding of PP‐EVA, which helped to enhance the interaction in the nanocomposites. The nanocomposites obtained from the direct clay strategy presented a co‐continuous morphology of bordering intercalated and agglomerated nanoclay sheets, while the nanocomposites obtained from the masterbatch strategy showed that blend morphology change from droplet to co‐continuous with the increase of EVA concentration, with intercalated/exfoliated nanoclay sheets located in the EVA domains and at the interface. The dynamic mechanical and creep‐recovery results showed different behavior for the both strategies in terms of chain mobility and relaxation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40897.     

Morphology and mechanical properties of heterophasic PP–EP/EVA/organoclay nanocomposites

The effect of vinyl acetat (VA) on the morphological, thermal stability, and mechanical properties of heterophasic polypropylene–(ethylene‐propylene) copolymer (PP–EP)/poly(ethylene vinyl acetate) (EVA)/organoclay nanocomposites was studied. Tailored organoclay C20A was selected to enhance the exfoliation of the clay platelets. Depending on the VA content, there were two morphological organoclay populations in the systems. Both populations were directly observed by scanning transmission electron microscopy and measured by wide‐angle X‐ray diffraction and small‐angle X‐ray scattering. The content of VA in EVA originated spherical and elongated morphologies in the resultant nanocomposites. High‐VA content led to a better intercalation of the organoclay platelets. Measurement of thermal properties suggested that higher VA decreases thermal stability in samples both with and without organoclay, although nanocomposites had higher thermal stability than samples without clay. The storage modulus increased both with nanoclay and VA content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Multiwall‐carbon‐nanotube‐reinforced poly(ethylene terephthalate) nanocomposites by melt compounding

Poly(ethylene terephthalate) (PET) nanocomposites reinforced with multiwall carbon nanotubes (MWCNTs) were prepared through melt compounding in a twin‐screw extruder. The presence of MWCNTs, which acted as good nucleating agents, enhanced the crystallization of PET through heterogeneous nucleation. The incorporation of a small quantity of MWCNTs improved the thermal stability of the PET/MWCNT nanocomposites. The mechanical properties of the PET/MWCNT nanocomposites increased with even a small quantity of MWCNTs. There was a significant dependence of the rheological properties of the PET/MWCNT nanocomposites on the MWCNT content. The MWCNT loading increased the shear‐thinning nature of the polymer‐nanocomposite melt. The storage modulus and loss modulus of the PET/MWCNT nanocomposites increased with increasing frequency, and this increment effect was more pronounced at lower frequencies. At higher MWCNT contents, the dominant nanotube–nanotube interactions led to the formation of interconnected or networklike structures of MWCNTs in the PET/MWCNT nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1450–1457, 2007     

Investigations on clay dispersion in polypropylene/clay nanocomposites using rheological and microscopic analysis

Morphology assessment plays an important role as the ultimate properties of the processed nanocomposites mainly depend upon the morphology. This study focuses on the evaluation of polypropylene/clay nanocomposite structure using rheological and transmission electron microscopic investigation. Melt processing of nanocomposite was carried out on a co‐rotating twin screw extruder. Maleic anhydride grafted polypropylene (PP‐g‐MA) was used as a compatibilizer to facilitate better mixing of clay in polypropylene. The effect of compatibilizer to clay ratio on dispersion was analyzed through rheological data. An increase in complex viscosity and storage modulus with increase in compatibilizer content is observed at lower frequency region. Shifting of crossover frequencies to a lower value also indicate better exfoliation. Improved exfoliated morphology was also corroborated by Cole–Cole and inverse loss tangent plots. Transmission electron microscopy (TEM) micrograph based unique statistical image analysis was carried out using ImageJ software. A compatibilizer to clay content of 2 : 1 was found to be the optimum composition which was further supported by dielectric and mechanical properties. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4464–4473, 2013     

Effects of different kinds of clay and different vinyl acetate content on the morphology and properties of EVA/clay nanocomposites

A series of EVA/clay nanocomposites and microcomposites have been prepared via melt-blending. Using four kinds of EVA with different vinyl acetate (VA) contents: 28, 40, 50 and 80 wt%, and four kinds of clay: three are organophilic clay (OMMT) and one unfunctionalized clay (Na-MMT), the effects of different VA content of EVA and the kinds of the clay on the morphology and properties of EVA/clay nanocomposites were systematically investigated. In previous studies, there are only two distinct nanostructures to distinguish polymer/clay nanocomposites: the intercalated and the exfoliated. But in this paper, we proposed a new nanostructure—‘the wedged’ to describe the dispersion degree of clay in nanocomposites, it means the sheets of clay were partly wedged by the chains of polymer. The wedged, the intercalated and the partially exfoliated structures of EVA/clay nanocomposites were characterized by X-ray diffraction (XRD) and by high-resolution transmission electron microscopy (HRTEM). The enhanced storage modulus of EVA/clay nanocomposites was characterized by dynamic mechanical thermal analysis (DMTA). The enhanced degree in the storage modulus of the OMMT on EVA/clay nanocomposites with the partially exfoliated and intercalated structure is much higher than that with wedged structure, and that with the higher VA content is higher than that with the lower. The thermal stabilities of EVA/clay nanocomposites were also studied by thermal gravimetric analysis (TGA).     

Effect of processing conditions on the structural morphology of PP–EP/EVA/organoclay ternary nanocomposites

The effect of processing conditions on the morphology of heterophasic PP–EP/EVA/organoclay ternary nanocomposites was examined. The nanocomposites were prepared in a co-rotating twin screw extruder with different screw configurations and incorporation methods. Three different sizes of EVA granules were used. The results obtained by X-ray scattering (WAXD) and electronic microscopy (TEM) showed an increase in d spacing value of the clay associated with the polar interactions between the vinyl acetate of EVA and the surface of the nanoclays. In addition, some chains of the non-polar copolymer PP–EP may have become intercalated into the clay galleries as a result of polymer diffusion induced by shear stress during melt mixing. An increase in surface area of EVA granules resulted in a more homogenous clay dispersion and intercalation. The morphologic changes resulted in an increase in heat distortion temperature (HDT) and flexural modulus of the ternary nanocomposites.     

Preparation of nanocomposites by melt compounding polylactic acid/polyamide 12/organoclay at different screw rotating speeds using a twin screw extruder

This study analyzes the effect of different screw rotating speeds on the clay dispersion and mechanical properties of nanocomposites prepared by melt compounding polylactic acid (PLA) with an organoclay in a co‐rotating twin screw extruder. Polyamide 12 (PA12) was used as an additive. Two different screw rotating speeds, 65 rpm and 150 rpm, were used in this study. According to the tensile strength data, the Young's modulus of the PLA/clay nanocomposites showed improvement at a screw rotating speed of 150 rpm. The Young's modulus improved with the addition of the organoclay to PLA matrix, but decreased when PA12 was added to the PLA matrix. The tensile strengths and elongations become small by adding organoclay to PLA matrix. The tensile strengths of the PLA/organoclay nanocomposites increased for the higher screw rotating speed (150 rpm). The d‐spacing of PLA/PA12/Clay nanocomposites was independent of the addition of PA12. The size of the clay aggregates in the PLA/PA12/Clay nanocomposites is smaller than that of PLA/Clay. Furthermore, the thermal stability of the PLA/Clay nanocomposite increases with addition of PA12, while on the whole, it had little influence on the tensile properties. POLYM. COMPOS., 29:1–8, 2008. © 2007 Society of Plastics Engineers     

Mechanical and thermal properties of toughened PA6/HDPE/SEBS‐g‐MA/Clay nanocomposite

Preparation and morphology of Polyamide 6 (PA6)/high density polyethylene (HDPE)/Styrene/Ethylene–Butylene/Styrene grafted with maleic anhydride (SEBS‐g‐MA)/Modified clay nanocomposites were studied. Mixing was performed using melting process in an extruder co‐rotating twin screw. After etching the materials with boiling toluene and THF at room temperature, the morphology of sample checked by scanning electron microscopy (SEM) analyses. X‐ray diffraction (XRD) used for evaluation of the effects of organo‐clay addition in the structure of nanocomposites. XRD traces showed that the characteristic (001) peak of the nanocomposites shifted to the lower degree region. XRD and SEM results showed more uniformly distribution and dispersion of HDPE in the PA6 matrix. Better sample morphology obtained, regarding less distance, and more uniformity between nanoparticles. The mechanical properties like tensile strength, impact strength, hardness and thermal properties of these toughened nanocomposites are discussed in terms of the nanoclay, SEBS‐g‐MA contents and morphology. Adding nanoclay improved hardness of nanocomposites product but reduced toughness and thermal properties. Meanwhile the presence of SEBS‐g‐MA as a compatibilizer improved toughness, thermal properties, hardness property, and the balance properties are achieved. POLYM. ENG. SCI., 55:29–33, 2015. © 2014 Society of Plastics Engineers     

Preparation and properties of nano‐CaCO3/acrylonitrile‐butadiene‐styrene composites

CaCO₃/acrylonitrile‐butadiene‐styrene (ABS) and CaCO₃/ethylene‐vinyl acetate copolymer (EVA)/ABS nanocomposites were prepared by melting‐blend with a single‐screw extruder. Mechanical properties of the nanocomposites and the dispersion state of CaCO₃ particles in ABS matrix were investigated. The results showed that in CaCO₃/EVA/ABS nanocomposites, CaCO₃ nanoparticles could increase flexural modulus of the composites and maintain or increase their impact strength for a certain nano‐CaCO₃ loading range. The tensile strength of the nanocomposites, however, was appreciably decreased by adding CaCO₃ nanoparticles. The microstructure of neat ABS, CaCO₃/ABS nanocomposites, and CaCO₃/EVA/ABS nanocomposites was observed by scanning electron microscopy. It can be found that CaCO₃ nanoparticles were well‐dispersed in ABS matrix at nanoscale. The morphology of the fracture surfaces of the nanocomposites revealed that when CaCO₃/EVA/ABS nanocomposites were exposed to external force, nano‐CaCO₃ particles initiated and terminated crazing (silver streak), which can absorb more impact energy than neat ABS. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of clay dispersion and content on the rheological,mechanical properties,and flame retardance of HDPE/clay nanocomposites

Full exfoliation of clay/high density polyethylene (HDPE) nanocomposites was successfully achieved with the aid of maleated HDPE (PE‐g‐MAn), by melt blending in a twin‐screw extruder employing a long residence time configuration. The morphology of the composites was determined using wide‐angle X‐ray diffraction and transmission electron microscopy. The effects of clay content and state of clay dispersion on the rheological, tensile properties, and flame retardancy of nanocomposites containing very small amounts of clay, in the range of 0.05–1.0 wt %, were investigated in this study. It was demonstrated that achieving a higher degree of exfoliation for nanosized clay particles is key to enhancing the rheological, mechanical, and flame retarding properties even when small amounts of clay (less than 1%) are used. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

The Effect of ultra‐high speed twin screw extrusion on ABS/organoclay nanocomposite blend properties

Acrylonitrile butadiene styrene (ABS) nanocomposites containing Cloisite 11 organoclay at 2 wt% were prepared using a 60 L/D ultra‐ high speed twin screw extruder (TSE), with speeds ranging from 400 to 4000 rpm. The purpose of this study was to investigate the effect of high shear melt processing on the intercalation and exfoliation of organoclay in the polymer, as well as the mechanical and rheological properties of the material. X‐ray Diffraction (XRD), and Transmission Electron Microscopy (TEM) results showed better intercalation of the nanofiller with increasing screw speed up to a point, and indicated an exfoliated structure of the nanocomposites extruded at 4000 rpm. Mechanical and rheological testing results indicated that by adding organoclay to ABS, the properties improved with increasing screw speed up to an optimum value of 2000 rpm. However, at the higher screw speeds of 3000 and 4000 rpm, the intense shear history led to a decrease in properties, most likely due to chain scission and molecular weight reduction. Similar trends were observed in rheological properties of the nanocomposite as well. At 2000 rpm, the results indicate that the lowering of the molecular weight due to shear effects is balanced by good intercalation/exfoliation of the organoclay. POLYM. ENG. SCI., 57:60–68, 2017. © 2016 Society of Plastics Engineers     

Rubber–clay nanocomposite by solution blending

Ethylene vinyl acetate rubber (45% vinyl acetate content, EVA‐45) and organomodified clay (12Me‐MMT) composites were prepared by solution blending of the rubber and the clay. A combination of X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy studies showed that the composites obtained are on the nanometer scale. The measurements of the dynamic mechanical properties for different compositions over a temperature range (?100 to +100°C) showed that the storage moduli of these rubber–clay nanocomposites are higher above the glass to rubber transition temperature compared to the neat rubber. The tensile strength of the nanocomposites is about 1.6 times higher than that of the EVA‐45. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2216–2220, 2003