Effects of process conditions and mixing protocols on structure of extruded polypropylene nanocomposites

Polymer melt‐direct intercalation or exfoliation is a promising approach for the preparation of nanocomposites. The structure of nanoclay platelets in the nanocomposites depends not only on the properties of polymer matrix and nanoclay, but also on the operating conditions during processing. The objective of the present work is to investigate the effects of clay chemical modifiers, mixing protocols, and operating conditions upon the clay structure in nanocomposites prepared with a corotating twin‐screw extruder. Two mixing methods were used for the nanocomposite preparation: two‐step mixing and one‐step mixing. Experimental results obtained from melt flow index and complex viscosity measurements suggest that nanoclay C15A is more exfoliated than C30B in a polypropylene homopolymer containing a maleic anhydride grafted PP (PB) as compatibilizer. The two‐step mixing method results in better exfoliation for the nanofillers than the one‐step mixing method. A numerical simulation has been carried out to evaluate the mean residence time and shear rate in different screw configurations under various process conditions. X‐ray diffraction experiments indicate that the residence time is a dominant factor in producing satisfactory nanocomposites in extruders. However, high shear rate coupled with long residence time might result in poor exfoliation of clay. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1891–1899, 2004     

Continuous process for melt intercalation of PP–clay nanocomposites with aid of power ultrasound

A continuous ultrasound‐assisted process using a single screw extruder with an ultrasonic attachment was developed to prepare PP/clay nanocomposites of varying clay concentrations. The feed rate that controlled the residence time of the polymer in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured. Rheological properties, morphology, and mechanical properties of the untreated and ultrasonically treated nanocomposites were studied. An intercalation of polymer molecules into clay galleries and a partial exfoliation, which occur at short residence times (of the order of seconds), were observed as evident from measurements by X‐ray diffraction and transmission electron microscopy. The obtained results indicate a possibility of the rapid intercalation and partial exfoliation of PP/clay nanocomposites without the matrix being chemically modified. J. VINYL. ADDIT. TECHNOL. 12:78–82, 2006. © 2006 Society of Plastics Engineers.     

Structure and melt rheology of long‐chain branching polypropylene/clay nanocomposites

Long‐chain branching polypropylene (LCB‐PP)/clay nanocomposites were prepared by melt blending in a twin‐screw extruder. The microstructure and melt rheology of these nanocomposites were investigated using x‐ray diffraction, transmission electron microscopy, oscillatory shear rheology, and melt elongation testing. The results show that, the clay layers are intercalated by polymer molecular chains and exfoliate well in LCB‐PP matrix in the presence of maleic anhydride grafted PP. Rheological characteristics, such as higher storage modulus at low‐frequency and solid‐like plateau in tan‐ω curve, indicate that a compact and stable filler network structure is formed when clay is loaded at 4 phr (parts per hundred parts of) or higher. The response of the nanocomposite under melt extension reveals an initial decrease in the melt strength and elongational viscosity with increasing clay concentration up to 6 phr. Later, the melt strength and elongational viscosity show slight increases with further increasing clay concentration. These results might be caused by a reduction in the molecular weight of the LCB‐PP matrix and by the intercalation of LCB‐PP molecular chains into the clay layers. Increases in the melt strength and elongational viscosity for the nanocomposites with decreasing extrusion temperature are also observed, which is due to flow‐induced crystallization under lower extrusion temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Rheological behavior of polypropylene/layered silicate nanocomposites prepared by melt compounding in shear and elongational flows

Melt rheology and processability of exfoliated polypropylene (PP)/layered silicate nanocomposites were investigated. The nanocomposites were prepared by melt compounding process in the presence or absence of a PP‐based maleic anhydride compatibilizer. PP/layered silicate nanocomposites showed typical rheological properties of exfoliated nanocomposites such as nonterminal solid‐like plateau behavior at low frequency region in oscillatory shear flow, higher steady shear viscosity at low shear rate region, and outstanding strain hardening behavior in uniaxial elongational flow. The melt processability of exfoliated PP/layered silicate nanocomposites was significantly improved due to good dispersion of layered silicates and increased molecular interaction between the PP matrix and the layered silicate organoclay. Small‐angle X‐ray scattering and transmission electron microscopy results revealed that the layered silicate organoclay was exfoliated and good interaction between PP matrix and organoclay was achieved by using the PP‐g‐MAH compatibilizer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3506–3515, 2007     

Exfoliation and dispersion enhancement in polypropylene nanocomposites by in‐situ melt phase ultrasonication

A novel process using ultrasonics to enhance the exfoliation and dispersion of clay platelets in polypropylene‐based nanocomposites has been proposed and investigated. The materials studied were isotactic polypropylene of various molecular weights reinforced with organophilic montmorillonite clay (nanoclay) at 4–6 wt% loadings. X‐ray diffraction (XRD) and rheological measurements, on a model system of nanoclay in mineral oil, were first used to determine ultrasonic energy requirements. The effectiveness of the proposed ultrasonic processing technique on polypropylene nanocomposites was evaluated by XRD and transmission electron microscopy (TEM). The effects of added maleic anhydride–grafted polypropylene compatibilizer, polypropylene molecular weight, and pretreatment of the nanoclays on the nanocomposite exfoliation were also investigated. Results indicate that ultrasonic processing of polymer nanocomposites in the melt state is an effective method for improving exfoliation and dispersion of nanoclays. Issues regarding molecular weight degradation, optimization, mechanical properties, and continuous processing are beyond the scope of the present study and are currently being investigated in our laboratory. Polym. Eng. Sci. 44:1773–1782, 2004. © 2004 Society of Plastics Engineers.     

Phase transformation and dielectric properties of polyvinylidene fluoride/organic-montmorillonite nanocomposites fabricated under elongational flow field

Compounding montmorillonite (MMT) with polymorphic polyvinylidene fluoride (PVDF) by melt intercalation method can induce the crystal phase transformation of PVDF, which is of great significance to obtain the electroactive PVDF. In this research, PVDF/Organic-Montmorillonite (OMMT) nanocomposites were prepared by a novel vane mixer, which was dominated by the elongational flow field in the whole plasticizing. The dispersion of OMMT, the crystal phase transformation of PVDF, and the resulting properties of nanocomposites were experimentally studied. The results of TEM and WAXD evidenced that homogeneous dispersion and desirable intercalation structure of OMMT were formed in the PVDF matrix under the effect of the elongational flow field. WAXD, FTIR, and DSC tests demonstrated that large amounts of β-phase of PVDF was formed due to the introduction of OMMT. The intercalation structure of OMMT and the crystal transformation of PVDF increased the dielectric constant and piezoelectric properties of nanocomposites, while the dielectric loss still maintained at a very low level. Finally, the effect of unique ''double-layer peeling'' mechanism of OMMT on the properties of nanocomposites was discussed.     

Thermoplastic polyurethane/polypropylene blends based on novel vane extruder: A study of morphology and mechanical properties

Thermoplastic polyurethane (TPU) polypropylene (PP) blends of different weight ratios were prepared with a self‐made vane extruder (VE), which generates global dynamic elongational flow, and a traditional twin‐screw extruder (TSE), which generates shear flow. The mechanical properties, phase morphology, thermal behavior, and spherulite size of the blends were investigated to compare the different processing techniques. Samples prepared with a VE had superior mechanical properties than the samples prepared with a TSE. Scanning emission micrographs show that the fiber morphology of the TPU/PP blends (<60 wt% TPU) was improved by elongational flow in VE. Differential scanning calorimetry curves indicate that a dynamical elongational flow could improve the miscibility of the TPU/PP blends. The U‐shaped spherulite size curve indicates the changes in the spherulite size, as observed from a polarization microscope. Interlocked spherulites also reveal the apparent partial miscibility of the TPU/PP blends under elongational flow. POLYM. ENG. SCI., 54:716–724, 2014. © 2013 Society of Plastics Engineers     

Development of EVOH-kaolinite nanocomposites

This paper reports on a novel route to develop EVOH-kaolinite nanocomposites by a melt intercalation process and on some relevant nanocomposite properties as a function of composition. The kaolinite clay used is a very cheap raw material of the tile industry and as such needed to be refined and chemically modified prior to the melt intercalation step. The modification was carried out with dimethyl-sulfoxide, methanol and octadecylamine in order to increase the basal plane distance of the original clay by a factor of more than three. Melt blended nanocomposites were characterized by WAXS, TEM, DSC, TGA and oxygen transmission rate. From the early results, partial exfoliation and intercalation of the clay platelets was the dominant morphology attained. An increase in thermal resistance, glass transition temperature, crystallinity and barrier properties to oxygen were also observed for mass clay loadings below 8%.     

Effect of clay amount and reprocessing cycles on thermal,morphological, and mechanical properties of polypropylene/organovermiculite nanocomposites

Nanocomposites of polypropylene (PP) and PP‐grafted‐maleic anhydride (PP‐g‐MA) with and without organophilic vermiculite (OVMT) (5–8%w/w) were evaluated. The nanocomposites and neat PP were submitted to extrusion reprocessing cycles. It was found that the presence of OVMT in PP/PP‐g‐MA was critical for maintaining thermal stability during reprocessing. The exfoliation/intercalation was confirmed, mainly, in the nanocomposite submitted to reprocessing cycles, by X‐ray diffraction. The melt flow index (MFI) values for the 3× and 5× reprocessed PP increased by 40% and 70%, respectively, as compared to the neat PP. The MFI for the 3× and 5× reprocessed PP/PP‐g‐MA/OVMT decreased 26% and 17%, respectively, as compared to the decrease occurred in the 3× and 5× reprocessed PP, indicating that the presence of 5% (w/w) OVMT was sufficient to allow an increase in viscosity. The reprocessed nanocomposites exhibited values for tensile and flexural strengths and Izod impact, in general, greater than or near to those of PP with the same number of reprocessing cycles. The increase or maintenance of mechanical properties seems to depend on a balance between the extent of intercalation/exfoliation and dispersion of OVMT in the PP matrix, and the degree of degradation of the PP matrix. POLYM. ENG. SCI., 59:2110–2120, 2019. © 2019 Society of Plastics Engineers     

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     

Batch and continuous processing of polymer layered organoclay nanocomposites

The generation of nanocomposites upon intercalation and exfoliation of clay tactoids using melt compounding is a difficult process. In this study various polymeric binders were melt compounded with organophilic clay particles using myriad methods, including sonication, batch mixing, and twin screw extrusion. The characterization of the compounded samples employing X‐ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that there is little intercalation and exfoliation when nonpolar poly(dimethyl siloxane) (PDMS) and poly(propylene) (PP) binders were used, resulting in no significant changes in the dynamic properties of the suspensions upon small‐amplitude oscillatory shearing. On the other hand, when polar polymeric binders, i.e., silanol terminated poly(dimethyl siloxane) and maleic anhydride modified PP were used for compounding with organoclays, TEM and XRD revealed intercalation with some partial exfoliation, resulting in increases in the dynamic properties, along with sensitivity to the thermomechanical history during processing. These results reinforce earlier findings, which suggest that the interfacial properties between the organoclays and the polymeric binders need to be tailored properly to enable the generation of nanocomposites of organoclays using melt compounding technologies. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1391–1398, 2007     

Dynamic mechanical,thermal, and morphological properties of silane‐treated montmorillonite reinforced polycarbonate nanocomposites

Three different loading of 3‐aminopropyltriethoxysilane (APS) was used to modify the Na‐montmorillonite via cation exchange technique. The Na‐MMT and silane‐treated montmorillonite (STMMT) were melt‐compounded with polycarbonate (PC) by using Haake Minilab machine. The PC nanocomposite samples were prepared by using Haake Minijet injection molding technique. The intercalation and exfoliation of the PC/MMT nanocomposites were characterized by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal properties of the PC nanocomposites were investigated by using dynamic mechanical analyzer and thermogravimetry analyzer. XRD and TEM results revealed partial intercalation and exfoliation of STMMT in PC matrix. Increase of APS concentration significantly enhanced the storage modulus (E′) and improved the thermal stability of PC nanocomposites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Nano/micro ternary composites based on PP,nanoclay, and CaCO3

Nano‐/microcomposites based on polypropylene/montmorillonite/calcium carbonate were prepared by melt mixing. Their structures and properties were characterized by small‐angle X‐ray diffraction, thermal analysis, and rheological measurements. The intercalation degree was found to be dependent on the compatibilizer content and the processing temperature. The addition of the organoclay slightly increased the melt crystallization temperature of polypropylene, acting as nucleating agents, and improved the degree of crystallinity. The rheological tests showed that nanocomposites increased the complex viscosity when compared with the microcomposites with the same filler content and exhibited a pronounced shear‐thinning behavior in the low frequency range. A Carreau‐Yasuda model was used to model the rheological behavior of these materials. The nano‐/microcomposites showed a significant improvement (about 50%) of the Young's modulus when compared with microcomposites with the same filler content due to the intercalation or exfoliation of the organoclay and the enhanced degree of crystallinity. Moreover, some formulations showed an enhancement of elongation at break and ultimate strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphological influence on mechanical characterization of ethylene‐vinyl acetate copolymer–clay nanocomposites

Ethylene‐vinyl acetate copolymer (EVA)/montmorillonite (MMT) clay nanocomposites with varying degree of intercalation and exfoliation have been prepared using direct melt blending techniques with various degrees of polarity (9, 18, and 28 wt% vinyl acetate [VA]) and two different types of clay modification. Morphological characterization using wide‐angle X‐ray scattering (WAXS) and transmission electron microscopy (TEM) have indicated/confirmed the presence of intercalation and/or a combination of intercalation and exfoliation existing in the nanocomposites. The effects of these (simple intercalation or mixed intercalation/exfoliation) states and the effect of changing matrix polarity (by changing VA wt% content) on the nanocomposite mechanical behavior were studied. There is sufficient evidence from the mechanical studies that 1) the presence of nanoclay can simultaneously improve modulus and strength of the nanocomposites, and 2) the mechanical properties are a combined function of the clay concentration and the nanocomposite morphology (due to the VA wt% and presence of clay). It is shown here that interrelation between the VA wt% content and the clay exfoliation affects the mechanical properties in a way that has a positive and increasing slope with increasing loading of clay. It is shown that a clear understanding of the nanocomposite mechanical properties can be obtained from its morphological analysis. POLYM. ENG. SCI., 45:889–897, 2005. © 2005 Society of Plastics Engineers     

Effect of Ionomeric Compatibilizer on Clay Dispersion in Polyethylene/Clay Nanocomposites

Summary: Linear low‐density polyethylene (LLDPE)/clay nanocomposites are obtained and studied by using a zinc‐neutralized carboxylate ionomer as a compatibilizer. LLDPE‐g‐MA is used as a reference compatibilizer. Two different clays, natural montmorillonite (Closite Na⁺) and a chemically modified clay Closite 20A have been used. Nanocomposites are prepared by melt blending in a twin‐screw extruder using two mixing methods: two‐step mixing and one‐step mixing. The relative influence of each compatibilizer is determined by wide‐angle X‐ray diffraction structural analysis and mechanical properties. The results are analyzed in terms of the effect of the compatibilizing agent and incorporation method in the clay dispersion, and the mechanical properties of the nanocomposites. Experimental results confirm that the film samples with ionomer show a good mechanical performance only slightly below that of the samples with maleic anhydride (MA). The two‐step mixing conditions result in better dispersion and intercalation for the nanofillers than one‐step mixing. The exfoliation of clay platelets leads to an improved thermal stability of the composite. The oxygen permeability of the clay nanocomposites, using ionomer as a compatibilizer, is decreased by the addition of the clay.

TEM image of a PE/4 wt.‐% Closite 20A nanocomposite formed using ionomer.     

The effect of clay type and of clay–masterbatch product in the preparation of polypropylene/clay nanocomposites

Clay containing polypropylene (PP) nanocomposites were prepared by direct melt mixing in a twin screw extruder using different types of organo‐modified montmorillonite (Cloisite 15 and Cloisite 20) and two masterbatch products, one based on pre‐exfoliated clays (Nanofil SE 3000) and another one based on clay–polyolefin resin (Nanomax‐PP). Maleic anhydride‐grafted polypropylene (PP‐g‐MA) was used as a coupling agent to improve the dispersability of organo‐modified clays. The effect of clay type and clay–masterbatch product on the clay exfoliation and nanocomposite properties was investigated. The effect of PP‐g‐MA concentration was also considered. Composite morphologies were characterized by X‐ray diffraction (XRD), field emission gun scanning electron microscopy (FEG‐SEM), and transmission electron microscopy (TEM). The degree of dispersion of organo‐modified clay increased with the PP‐g‐MA content. The thermal and mechanical properties were not affected by organo‐modified clay type, although the masterbatch products did have a significant influence on thermal and mechanical properties of nanocomposites. Intercalation/exfoliation was not achieved in the Nanofil SE 3000 composite. This masterbatch product has intercalants, whose initial decomposition temperature is lower than the processing temperature (T ～ 180°C), indicating that their stability decreased during the process. The Nanomax‐PP composite showed higher thermal and flexural properties than pure PP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and interaction characteristics of exfoliated ABS/organoclay nanocomposite

A series of poly(acrylonitrile‐co‐butadiene‐co‐styrene) (ABS)/organoclays (Cloisite10A, Cloisite25A, and Cloisite30B) nanocomposites are prepared via two different methods: one is a solution blending and the other is a two‐step process where the solution blended mixture is subsequently compounded in the melt state using a torque rheometer (SOAM method). The effect of surfactants on the surface of three different organoclays that are modified with alkylammonium salts in polymer/organoclay nanocomposites is investigated by focusing on two major aspects; Flory‐Huggins interaction parameters and physical (thermal and mechanical) properties. The d‐spacing of both neat organoclays and intercalated/exfoliated organoclays is examined by X‐ray diffraction analysis, and the microstructure of these nanocomposites is examined by FE‐TEM. Solubility parameters of both polymer and organoclays of interest are calculated according to the group contribution method. Viscoelastic behavior of the nanocomposites is also investigated by measuring rheological properties under an oscillatory shear. The increase in the onset temperature of the thermal degradation indicates the enhancement of thermal stability of ABS due to intercalation or partial exfoliation. Mechanical properties, such as, tensile strength, tensile modulus, and elongation at break of the nanocomposites are measured. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Effect of processing conditions on morphology and mechanical properties of compatibilized polypropylene nanocomposites

This work focuses on the influence of processing conditions on the nanocomposites structure, i.e. intercalated or exfoliated, and on the enhancement of mechanical properties of polypropylene (PP) nanocomposites. These nanocomposites were prepared using the melt intercalation technique in a co-rotating intermeshing twin screw extruder. In order to optimise processing conditions, both screw speed and barrel temperature profile were changed. The role of the compatibilizer (maleic anhydride grafted polypropylene) was also studied. The results obtained show that the barrel temperature is a very important parameter: using lower processing temperature, the apparent melt viscosity and, consequently, the shear stress are higher and, therefore, the exfoliation of the clay is promoted. Even using optimised processing conditions, exfoliation of clay can be achieved only when an high compatibility between polymer and clay exists: the PP nanocomposites containing maleic anhydride show an exfoliated structure and a sensible enhancement of mechanical properties while PP nanocomposites without compatibilizer show a structure mainly intercalated and a lower improvement of mechanical properties.     

Ultrasound aided extrusion process for preparation of polyolefin–clay nanocomposites

A continuous ultrasound assisted process using a single screw compounding extruder with an ultrasonic attachment was developed to prepare polyolefin/clay nanocomposites. High‐density polyethylene and isotactic polypropylene were compared. The feed rate that controls the residence time of the polymer in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured. Rheological properties, morphology, and mechanical properties of the untreated and ultrasonically treated nanocomposites were studied. Similarities and differences of obtained nanocomposites are discussed based on their properties and structural characteristics. The modified Halpin‐Tsai theory of composite materials has been employed in order to predict the effect of incomplete exfoliation of clay platelets on the Young's modulus of the nanocomposites. A good agreement between experimental and theoretical data has been observed when reduction of the reinforcement efficiency of clay had been incorporated through the reduced aspect ratio of elementary clay platelets. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Study of polypropylene/poly(ethylene terephthalate) bicomponent melt‐blowing process: The fiber temperature and elongational viscosity profiles of the spinline

Although there are significant differences between high‐speed melt spinning and melt blowing (MB), they are similar in many important components. This study, motivated by the need to better understand the bicomponent MB process, used the basic theories of high‐speed melt spinning to estimate the fiber temperature and elongation viscosity profiles of the polypropylene/poly(ethylene terephthalate) (PP/PET) bicomponent MB process. During the MB process, the filament temperature decreased dramatically within the first 2 in. from the MB die. The fiber temperature‐decay profiles of PP, PET monocomponent, and PP/PET bicomponent filaments followed similar trends. PP filaments attenuated faster than PET filaments and the bicomponent filaments attenuated at a medium rate between that of PP and PET. Accordingly, the elongational viscosity increased significantly in the first 2 in. from the die. PET filaments exhibited higher elongational viscosity than that of 100% PP filaments. The elongational viscosity profile of 75%PP/25%PET was between that of PP and PET monocomponent filaments. These data provided important information on understanding the MB process and filament attenuation. It also suggested that the filament elongational viscosity profile is the key factor in production of finer bicomponent MB fibers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1145–1150, 2003