PE/clay nanocomposites produced via in situ polymerization by highly active clay-supported Ziegler–Natta catalyst

The synthesis of polyethylene/clay (PE/clay) nanocomposites by means of in situ polymerization was achieved using the clay/BOM/chloroform/EtOH/TiCl₄/TEA catalyst system where butyl octyl magnesium (BOM) and triethyl aluminum (TEA) were a modifier for the clay and cocatalyst, respectively. It was found that the catalyst had high activity in ethylene polymerization. The microstructure of the resulting PE/clay nanocomposites was characterized by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The examinations evidenced the nanocomposite formation with exfoliated clay in the PE matrix. The thermal properties of the produced nanocomposites were studied by differential scanning calorimetry, oxidation induction time, and thermal gravimetric analysis. Furthermore, the mechanical properties of the nanocomposites were evaluated by the impact and tensile tests. The examinations indicated the improved thermal stability and mechanical properties. Meanwhile, a wide range of molecular weights were produced in the presence of hydrogen.     

In Situ Synthesis of Ultrahigh Molecular Weight Polyethylene/Graphene Oxide Nanocomposite Using the Immobilized Single-site Catalyst

We address the immobilization of single-site catalyst on the graphite oxide (GO) surface using methylaluminoxane. Ethylene polymerization was performed using the immobilized catalyst and the nanocomposite of ultrahigh molecular weight polyethylene (UHMWPE)/GO with less entanglement density was obtained. It was observed that the drawability, mechanical and thermal properties of the produced polymer significantly are affected by the anchoring of polymer chains to the GO nanosheets. The orientation and location of crystalline lamellae and nanosheets were verified by microscopic techniques. Besides, X-ray analysis demonstrated the dispersion of GO within the UHMWPE phase and crystallinity of UHMWPE/GO nanocomposites enhanced during drawing process.     

Polymerization kinetics and thermal properties of dicyanate/clay nanocomposites

The polymerization kinetics and thermal properties of dicyanate/clay nanocomposites were investigated. A type of organically modified clay was used as nanometer‐size fillers for the thermosetting dicyanate resin. Differential scanning calorimetry (DSC) was used to study the curing behavior of the dicyanate/clay nanocomposite systems. The polymerization rate of the nanocomposite systems increased with increasing clay content. An autocatalytic reaction mechanism could adequately describe the polymerization kinetics of the dicyanate/clay nanocomposite systems. The polymerization kinetic parameters were determined by fitting the DSC conversion data to the proposed kinetic equation. The glass‐transition temperature of the dicyanate/clay nanocomposites increased with increasing clay content. The thermal decomposition behavior of the dicyanate/clay nanocomposites was investigated by thermogravimetric analysis. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1955–1960, 2004     

Synthesis and characterization of poly(styrene‐co‐butyl acrylate)/clay nanocomposite latexes in miniemulsion by AGET ATRP

Polymer/clay nanocomposite latexes in the form of positively charged nanoparticles were synthesized by a newly developed initiating system, activators generated by electron transfer (AGET), which has been employed in atom transfer radical polymerization (ATRP). These clay‐dispersed latexes were synthesized using AGET ATRP of styrene and butyl acrylate in a miniemulsion system in which, ascorbic acid as a reducing agent was added drop wise to reduce termination reactions. Particle size and particle size distribution of resulted nanocomposite latexes were characterized by dynamic light scattering (DLS). These latexes were in the range of 138 to 171 nm in size. Gel permeation chromatography (GPC) was used to characterize the molecular weight and molecular weight distribution of the resultant copolymer nanocomposites. GPC traces showed that polymers of narrow molecular weight distribution and low Polydispersity Index (PDI) have been synthesized; this clearly shows ATRP reaction is conducted successfully. By increasing nanoclay content, molecular weight of the nanocomposites decreases. The presence of the nanofiller increases the thermal stability of the nanocomposites as investigated by thermogravimetric Analysis (TGA). Glass transition temperature of nanocomposites increases compared with the neat copolymer which was studied by differential scanning calorimetry (DSC). scanning electron microscope (SEM) showed sphere morphology of polymer particles synthesized by miniemulsion polymerization. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that mixed intercalated and exfoliated morphology is obtained. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

In situ polymerization of polyethylene/clay nanocomposites using a novel clay‐supported Ziegler‐Natta catalyst

Polyethylene/clay nanocomposites (PECNC) were synthesized via in situ Ziegler‐Natta catalyst polymerization. Activated catalyst for polymerization of ethylene monomer has been prepared at first by supporting of the cocatalyst on the montmorillonite (MMT) smectite type clay and then active complex for polymerization formed by reaction of TiCl₄ and aluminum oxide compound on the clay. Acid wash treatment has been used for increasing hydroxyl group and porosity of the clay and subsequently activity of the catalyst. The nanostructure of composites was investigated by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Obtained results show that silica layers of the mineral clay in these polyethylene/nanocomposites were exfoliated, intercalated, and uniformly dispersed in the polyethylene matrix even at very high concentration of the clay. Thermogravimetric analysis (TGA) shows good thermal stability of the PECNCs. Differential scanning calorimeter (DSC) results reveal considerable decrease in the crystalline phase of the PECNC samples. Results of permeability analysis show an increase in barrier properties of PECNC films. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Polyethylene and polypropylene nanocomposites based on polymerically-modified clay containing alkylstyrene units

Sodium montmorillonite was modified with a new polymeric surfactant. The high molecular weight of the surfactant appears to have led to incomplete cation exchange of the clays, but did promote nanocomposite formation with polyethylene and polypropylene. X-ray diffraction combined with transmission electron microscopy revealed a mixed nanocomposite morphology. The thermal stability of the nanocomposites was evaluated by thermogravimetric analysis, while flammability of the nanocomposites was evaluated by cone calorimetry. A significant 40% reduction in peak heat release rate was observed at 10% organo-clay (3% inorganic clay) loading with an even higher 50% reduction at a loading level of 16% modified clay (5% inorganic clay). Despite possible plasticization effects by the polymers used as an organic modification for the clays, the mechanical properties such as Young's modulus and elongation were not severely impacted by the nanocomposite formation.     

Effect of milling time and clay content on the thermal stability of polyethylene‐clay nanocomposite

The aim of the paper was to investigate the thermal properties of polyethylene (PE)‐clay nanocomposites prepared via the high energy ball milling (HEBM) method. The structure and morphology of the nanocomposites were examined by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Thermal stability of all milled samples, including pure PE and PE‐clay nanocomposites was measured by thermal gravimetric analysis (TGA). The effect of milling time and clay contents on the thermal stability of PE was investigated. The results show that the thermal stability of PE promotes with increasing milling time. Clay has two opposed functions in the thermal stability of the nanocomposite, the first one is the barrier effect to improve the thermal stability, and another one is the catalysis effect leading to a decrease of the thermal stability. J. VINYL ADDIT. TECHNOL., 22:285–292, 2016. © 2014 Society of Plastics Engineers     

BCE催化剂制备双峰PE的研究

研究开发了BCE高效聚乙烯催化剂．并模拟超临界工艺制备出双峰聚乙烯树脂。BCE催化剂具有较高的活性（约为参考催化剂的2倍）和良好的氢调敏感性;与参考催化剂相比,该催化剂制备的聚乙烯树脂具有较高的堆积密度（0．39g／cm^3）和较窄的相对分子质量分布,重均分子量低于1000的部分较少。     

Polyethylene-layered silicate nanocomposites prepared by the polymerization-filling technique: synthesis and mechanical properties

Polyethylene-layered silicate nanocomposites were prepared by the in situ intercalative polymerization of ethylene by the so-called polymerization-filling technique and analyzed by transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), differential scanning calorimetry, dynamic mechanical analysis and tensile testing. Non-modified montmorillonite and hectorite were first treated by trimethylaluminum-depleted methylaluminoxane before being contacted by a Ti-based constrained geometry catalyst. The nanocomposite was formed by addition and polymerization of ethylene. In the absence of a chain transfer agent, ultra high molecular weight polyethylene was produced. The tensile properties of these nanocomposites were poor and essentially independent of the nature and content of the silicate. Upon hydrogen addition, the molecular weight of the polyethylene was decreased with parallel improvement of the tensile and shear moduli, in relation to the filler content. The exfoliation of the layered silicates was confirmed by XRD analysis and TEM observation. The mechanical kneading of the molten nanocomposites resulted in the partial collapse of the exfoliated structure driven by the thermodynamic stability of the layered filler.     

宽峰聚乙烯／蒙脱土纳米复合材料的制备

利用2种不同的方法制备了2种氢调敏感性不同的蒙脱土／氯化镁／四氯化钛（MMT／MgCl2／TiCl4）催化剂,利用这2种催化剂及其混配催化剂,通过原位聚合法,制备出一系列宽峰聚乙烯纳米复合材料,采用X_射线衍射仪（XRD）、凝胶色谱测试分析（GPC）及力学性能测试等方法对催化剂及聚合产物进行分析,结果表明,2种催化剂以及按照不同比例混合的混配催化剂均表现出较高的聚合活性,XRD测试结果表明,蒙脱土片层在乙烯聚合过程中发生了插层及剥离,以单片层或几层共存的形式分散于聚乙烯基质中;用混配催化剂可制得宽峰聚乙烯纳米复合材料,Mw／Mn=7．23,并且聚合物的堆积密度达到工业生产的标准,宽峰聚乙烯纳米复合材料的综合力学性能较工业产品5000S及工业上应用的管材料有很大的提高。     

Preparation of polystyrene–clay nanocomposites via dispersion polymerization using oligomeric styrene‐montmorillonite as stabilizer

This study describes the preparation of polystyrene–clay nanocomposite (PS‐nanocomposite) colloidal particles via free‐radical polymerization in dispersion. Montmorillonite clay (MMT) was pre‐modified using different concentrations of cationic styrene oligomeric (‘PS‐cationic’), and the subsequent modified PS‐MMT was used as stabilizer in the dispersion polymerization of styrene. The main objective of this study was to use the clay platelets as fillers to improve the thermal and mechanical properties of the final PS‐nanocomposites and as steric stabilizers in dispersion polymerization after modification with PS‐cationic. The correlation between the degree of clay modification and the morphology of the colloidal PS particles was investigated. The clay platelets were found to be encapsulated inside PS latex only when the clay surface was rendered highly hydrophobic, and stable polymer latex was obtained. The morphology of PS‐nanocomposite material (after film formation) was found to range from partially exfoliated to intercalated structure depending on the percentage of PS‐MMT loading. The impact of the modified clay loading on the monomer conversion, the polymer molecular weight, the thermal stability and the thermomechanical properties of the final PS‐nanocomposites was determined. Copyright © 2012 Society of Chemical Industry     

Preparation and characterization of polyethylene (PE)/clay nanocomposites by <Emphasis Type="Italic">in situ</Emphasis> polymerization with vanadium-based intercalation catalyst

Summary  Complete exfoliation of clay during vanadium-based Zigler-Natta polymerization of ethylene has been successfully carried out by using clay and MgCl₂ hybrid supports. MgCl₂ offers catalyst loading sites, and the vanadium catalyst is avoided directly anchoring in the surface of the clay, so intercalation catalyst clay/MgCl₂/VOCl₃displays high activity for ethylene polymerization. Exfoliated PE/clay nanocomposites are confirmed by X-ray diffraction (XRD), and transmission electron microscopy (TEM). Strong interaction between the dispersed clay particles and the polymer matrices provides good thermal and mechanical properties. Compared with pure PE, all these nanocomposites show enhancement of the melting temperature (T_m) and the thermal decomposition temperatures. Additionally, the incorporation of clay into the PE matrix significantly improves the mechanical properties of these nanocomposites. The increased tensile strength has been observed in the range of 3.4 to 7.9 MPa. The tensile moduli of the PE/clay nanocomposite are 23.4%-45.3% higher than that of the pure PE.     

Catalytic activity during the preparation of PE/clay nanocomposites by in situ polymerization with metallocene catalysts

Catalytic activity during the formation of polyethylene (PE)/clay nanocomposites by in situ polymerization with metallocenes was studied. Ethylene polymerization was carried out with the homogeneous metallocene in the presence of the clay particles and using the clay‐supported metallocene catalyst. It was found that the catalytic activity of the homogeneous metallocene does not decrease in the presence of the clay particles and only a slight decrease of activity occurs using the clay‐supported catalyst. The modification of the clay with MAO cocatalyst as well as its intercalation with ODA surfactant were found to play an important role during the in situ formation of the PE/clay nanocomposite. ODA‐intercalated clay apparently facilitates the activation and monomer insertion processes on zirconocene centers located in internal sites of the clay structure. Although metallocene supported on MAO‐treated clay exhibited somewhat lower catalytic activity than that supported directly on the ODA‐intercalated clay, both systems favored the production of PE nanocomposites containing highly exfoliated clay particles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and characterization of polyimide/organoclay nanocomposites

Organically modified montmorrillonite clay, containing a long chain aliphatic quarternary ammonium cation, was used to prepare polyimide/organoclay hybrids. Several approaches were examined in an attempt to achieve fully exfoliated nanocomposites. These included simple mixing of the clay in a pre-made high molecular weight poly(amide acid) solution; simple mixing followed by sonication of the organoclay/poly(amide acid) solutions; and the preparation of high molecular weight poly(amide acid)s in the presence of the organoclay dispersed in N-methyl-2-pyrrolidinone (NMP). The best results were obtained using the in-situ polymerization approach. The resulting nanocomposite films (both amide acid and imide), containing 3-8% by weight of organoclay, were characterized by differential scanning calorimetry (DSC), dynamic thermogravimetric analysis (TGA), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thin film tensile properties. A significant degree of dispersion was observed in the nanocomposite films of the amide acid and the imide. After thermal treatment of amide acid films to effect imidization, in both air and nitrogen, the films were visually darker than control films without clay and the level of clay dispersion appeared to have decreased. In the latter case, the separation between the layers of the clay decreased to a spacing less than that present in the original organoclay. These observations suggest that thermal degradation of the aliphatic quarternary ammonium cation occurred likely during thermal treatment to effect imidization and solvent removal. These thermal degradation effects were less pronounced when thermal treatment was performed under nitrogen. The polyimide/organoclay hybrid films exhibited higher room temperature tensile moduli and lower strength and elongation to break than the control films.     

Novel LDPE/vermiculite/ciclopiroxolamine hybrid nanocomposites: Structure,surface properties,and antifungal activity

The increasing number of indwelling medical materials and devices are connected with infections caused by yeast, especially Candida albicans. This pathogen produces biofilms on synthetic materials, which facilitates adhesion of the organisms to devices and renders them relatively refractory to medical therapy. Since antimicrobial polymer nanocomposites present one of the promising possibilities, this study explores a new approach to achieving this goal by developing nanocomposite based on low density polyethylene (LDPE) with clay mineral vermiculite as an active carrier for antifungal compound. The set of LDPE/clay nanocomposite with increasing amount of antifungal nanofiller was prepared by melt compounding procedure. As antifungal agent was selected generally used active substance ciclopiroxolamine and this compound was loaded into natural vermiculite through ultrasound technique. The structure of all prepared samples was studied by X-ray diffraction analysis and Fourier transforms infrared spectroscopy. Further thermal properties of polyethylene/clay nanocomposites were investigated by thermogravimetric analysis and the surface properties were evaluated by light optical microscopy, scanning electron microscopy and atomic force microscopy. From mentioned characteristics, we conclude that presence of nanofiller in LDPE primarily causes shift of thermal degradation to higher temperatures and increasing of microhardness. All prepared LDPE nanocomposites possess an excellent and prolonged antifungal activity against Candida albicans.     

Synthesis and characterization of clay dispersed polystyrene nanocomposite via atom transfer radical polymerization

Finely well‐defined polystyrene nanocomposites were prepared by ATRP method in bulk at 110°C using organically modified montemorillonite, cloisite 30B. The living nature of ATRP reaction was employed to in situ synthesize tailor‐made polystyrene nanocomposite with narrow molecular weight distribution and controlled molecular weight polystyrene chains. The amount of clay loading and time of swelling of clay in the monomer before polymerization were proved to have a positive effect on polymerization rate and also broadened the molecular weight destribution. The gas chromatography (GC) results showed the linear increase of Ln(M₀/M) versus time, which indicates the controlled/living polymerization in the presence of nanoclay. Another confirmation of the living nature of the polymerization was linear elevation of molecular weight against monomer conversion concluded from gel permeation chromatography (GPC) data. X‐ray diffraction analysis showed the interlayer spacing of nanoclay platelets as well as the exfoliated clay morphology in the nanocomposite samples. Transfer electron microscopy (TEM) revealed the exfoliated morphology of the in situ prepared nanocomposite as opposed to conventional solution‐blending technique which resulted in an intercalated structure. The effect of nanoclay on acceleration of polymerization was proved by GC and GPC; similarly, Fourier transform infrared spectroscopy (FTIR) was used to discuss the reasons of such a rate acceleration. A shifting in the wave number of characteristic bonds of nanoclay after polymerization mostly in the case of O H and Si O bonds, revealed the interaction between polymer chains and clay layers which resulted in an accelerated polymerization process. The living nature of polymeric chains was more elucidated by FTIR data. Atomic force microscopy (AFM) images also confirmed the proper dispersion of nanoparticles in the polymer medium. POLYM. COMPOS., 31:1829–1837, 2010. © 2010 Society of Plastics Engineers     

In situ polymerization of ethylene with functionalized multiwalled carbon nanotubes using a zirconocene aluminohydride system in solution

This study reports nanocomposite synthesis based on high-density polyethylene with carbon nanotubes through in situ polymerization by coordination, and the use of an aluminohydride zirconocene/MAO system as a catalyst. Nanocomposites of linear polyethylene exhibit higher molar masses than pure high-density polyethylene synthesized under similar conditions; where multiwalled carbon nanotubes (MWCNTs) acted as nucleating agents, shifting the crystallization temperature to higher values than neat high-density polyethylene. Well-dispersed MWCNTs in the HDPE matrices of the obtained nanocomposites are observed by SEM, where most of the nanocomposites showed an improvement in their thermal stability and electric conductivity, besides it is possible to obtain nanocomposites containing up to 41 wt% of nanofiller in the polymeric matrix. The aluminohydride complex n-BuCp₂ZrH₃AlH₂, activated with MAO at Al/Zr ratios of 2000, produced homogeneous HDPE/MWCNT composites under in situ polymerization conditions, at 70°C and 2.9 bar of ethylene pressure, with minimal residual alumina in the HDPE matrix.     

Effect of organomodified clay on the reaction kinetics,properties and thermal degradation of nanocomposites based on poly(styrene‐co‐ethyl methacrylate)

In this research, synthesis of novel nanocomposites based on a poly(styrene‐co‐ethyl methacrylate) copolymer matrix was investigated with different types and amounts of organomodified montmorillonite (MMT) clays. The in situ polymerization technique was selected with dispersion of the MMT nanoparticles into the comonomer mixture and subsequent bulk radical polymerization. Reaction kinetics was measured gravimetrically and it was found that the existence of rigid phenyl rings in the organomodifier may result in a hindered reaction rate especially at high clay loadings. Structural characteristics of the nanocomposites formed were verified with XRD and Fourier transform infrared analysis and mainly intercalated/partially exfoliated structures were verified; their glass transition temperature was measured with DSC, and their molecular weight distribution and average molecular weights were measured with gel permeation chromatography. The latter was also used to measure the variation of the copolymer average molecular weight with conversion. Slightly higher average molecular weight and T_g values for the copolymer in the nanocomposites were measured, compared with neat copolymer. The thermal stability of the nanocomposites was measured with TGA and found to be significantly improved. One‐step degradation revealed the existence of macromolecular chains without defective structures. Finally, pyrolysis of the nanocomposite copolymers resulted in the production of both comonomers in high amounts, followed by some dimers or trimers. © 2013 Society of Chemical Industry     

Thermal and Morphological Properties of Organo Modified Nanoclay/Polyethylene Terephthalate Composites

The purpose of this study is polyethylene terephthalate (PET) and modified organo-nanoclay with different masses and to contribute to the different areas of use and literature by examining these nanocomposites physical, chemical and thermal features. In this study, nanocomposite films, which work in PET that is a type of polymeric material, and work into modified organo-nanoclays with different percentages, obtained with the method called as in situ polymerization. The chemical structures of nanocomposites prepared were investigated by fourier transform infrared spectroscopy. The surface morphologies of this nanocomposites were examined by scanning electron microscope. Their thermal properties were analyzed by differential scanning calorimetry and thermogravimetric analysis. According to the results obtained, the thermal stabilities of modified nanoclay composites got better than PET. Besides, while the percent of clay in the doped PET was rising, its fragility increased. At the same time, high mass of clay formed when the percent of contribution developed. Thus, the surface interaction of polymer–clay decreased, because the composed aggregations prevented the polymer matrix from going into the layer of clay.     

Effect of nanoclay type on dyeability of polyethylene terephthalate/clay nanocomposites

Polyethylene terephthalate (PET)-based nanocomposites containing three differently modified clays were prepared by melt compounding. The influence of type of clay on disperseability, thermal, and dyeing properties of the resultant nanocomposite was investigated by various analytic techniques, namely, X-ray diffraction, optical microscopy (OPM), differential scanning calorimetry, thermal gravimetric analysis, dynamical mechanical thermal analysis, contact angle measurement (CAM), reflectance spectroscopy, and light fastness. OPM images illustrated formation of large-sized spherulites in pure PET, while only small-sized crystals appeared in PET/clay nanocomposites. Decreased glass transition temperatures for all PET/clay nanocomposites indicate that the amorphous regions of such composites become mobile at lower temperatures than those in pure PET. CAMs on the resultant PET composites demonstrated that the wettability of such composites depends on hydrophilicity of the nanoclay particles. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012