Supercritical carbon dioxide (scCO2) dispersion of poly(ethylene terephthalate)/clay nanocomposites: Structural,mechanical, thermal,and barrier properties

Dispersed poly(ethylene terephthalate) (PET)/clay nanocomposites can lead to materials with superior barrier and mechanical properties. PET/clay nanocomposites were prepared by melting extrusion of PET with as‐received or supercritical carbon dioxide (scCO₂) predispersed Cloisite^® 30B (30B). The predispersion of 30B was assessed by WAXD, SEM, and TGA, and results indicated that scCO₂ processing could predisperse 30B and the surface modification of the clay was preserved after processing. The structure of PET/30B nanocomposites was investigated by WAXD and TEM confirming that PET has penetrated into the clays inter‐galleries and the predispersed clays lead to improved interfacial interaction and homogenous clay dispersion. Both tensile strength and Young's modulus were improved by 12.1% and 24.9% respectively, as incorporating of 3 wt % of scCO₂ processed clay. Differential scanning calorimetry (DSC) results indicated that clay particles served as nucleation agent could increase the crystallinity whereas had no impact on melting process. In addition, with the addition of 1 wt % of predispersed clay, a significant reduction of oxygen permeation (～33%) was achieved at 23 °C and the maximum reduction (44%) was achieved by adding 3 wt % processed clay. Moreover, we confirmed the effect of temperature on the permeation of PET/30B nanocomposites depended both on the Arrhenius behavior of the organic phases and tortuous path effects, where improved clay dispersion resulted in a higher effective activation energy. Moreover, the transparency of PET matrix was preserved for all nanocomposites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44779.     

Preparation and characterization of PET/clay nanocomposites by melt compounding

Poly(ethylene terephthalate) (PET) nanocomposites were prepared via melt compounding using a twin‐screw extruder at 265°C. Three different types of organomodified clay were melt compounded with PET: a commercial ammonium‐modified silicate clay (Cloisite 30B) and specially prepared thermally stable phosphonium‐ and imidazolium‐modified montmorillonites. X‐ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), and thermogravimetric analysis were used to characterize and evaluate the quality of the nanocomposites. To obtain quantitative evaluation of the dispersion level in nanocomposites, statistical analysis of TEM micrographs was performed using a dispersion parameter, D_0.1, based on free‐path spacing measurements. The results showed that the ammonium surfactant yielded the best intercalation results in nanocomposites. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

A Model for Molecular Weight Prediction in Acrylonitrile Polymerization

Poly ethylene terephthalate (PET)-based nanocomposites containing three differently modified clays were prepared by melt compounding. The influence of type of modified clay on surface properties of the resultant nanocomposite was investigated by various analytic techniques, namely, Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), contact angle measurement (CAM), scanning electron microscopy (SEM) and reflectance spectroscopy (RS). Any possible interaction between each nanoclay and PET at the surface was elucidated by Fourier transform infrared spectroscopy. Atomic force microscopy studies of the resultant nanocomposites showed increased in surface roughness compared to pure PET. Contact angle measurements on the resultant PET composites demonstrated that the wettability of such composites depends on hydrophilicity of the nanoclay particles. Scanning electron microscopy images illustrated poor interfacial interaction between PET and Na⁺ clay particles causing fracture type non-uniformity of PET/Na⁺ clay nanocomposite.     

PET‐ionomers and PETi/MMT nanocomposites: A comparison of the effect of ionic groups on their crystallinities and physical properties

Poly(ethylene terephthalate) (PET) and PET/modified montmorillonite (A10‐MMT) nanocomposites containing up to 3 mol% of dimethyl 5‐sulfoisophthalte sodium salt (DMSi) were prepared by in situ polymerization (PETi and PETNi, respectively). In results from transmission electron microscopy (TEM, ∼ 10 nm), clusters were observed with sizes of 30 nm at an ionic content of 3 mol%. Clusters were not observed in the PETNi samples due to the favorable interaction between the positively charged edges of the clay platelets and the negatively charged ionic groups. On the other hand, the degree of exfoliation was considerably improved by the small ionic content. Remarkable increases in the storage moduli of PETi and PETNi were also observed with increasing DMSi content in the glassy region. However, the storage modulus of PETi decreased rapidly in the rubbery region above the transition temperature as temperature increased. The dynamic viscosity of PETNi decreased with DMSi content, indicating that ion‐pair sites located at the clay edges acted as selective plasticizers in the PET ionic region. Moreover, the introduction of a small ionic content into the PET matrix led to a decrease in crystallinity and slower crystallization rates than in the pure PET. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Synthesis and properties of BCDA‐based polyimide–clay nanocomposites

Bicyclo[2.2.2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride (BCDA)‐based polyimide–clay nanocomposites were prepared from their precursor, namely polyamic acid, by a solution‐casting method. The organoclay was prepared by treating sodium montmorillonite (Kunipia F) clay with dodecyltrimethylammonium bromide at 80 °C. Polyamic acid solutions containing various weight percentages of organoclay were prepared from 4,4′‐(4,4′‐isopropylidenediphenyl‐1,1′‐diyldioxy)‐dianiline and BCDA in N‐methyl‐2‐pyrrolidone containing dispersed particles of organoclay at 20 °C. These solutions were cast on a glass plate using a Doctor's blade and then heated subsequently to obtain nanocomposite films. The nanocomposites were characterized using Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal mechanical analysis, dynamic mechanical analysis, polarizing microscopy, scanning electron microscopy, transmission electron microscopy, wide‐angle X‐ray diffraction (WAXD) and thermogravimetric analysis. The glass transition temperature of the nanocomposites was found to be higher than that of pristine polymer. The coefficient of thermal expansion of the nanocomposites decreased with increasing organoclay content. WAXD studies indicated that the extent of silicate layer separation in the nanocomposite films depended upon the organoclay content. Tensile strength and modulus of the nanocomposite containing 1% organoclay were significantly higher when compared to pristine polymer and other nanocomposites. The thermal stability of the nanocomposites was found to be higher than that of pristine polymer in air and nitrogen atmosphere. Copyright © 2007 Society of Chemical Industry     

Effect of water‐assisted extrusion and solid‐state polymerization on the microstructure of PET/Clay nanocomposites

An melt‐mixing process has been used to prepare Poly(ethylene terephthalate) (PET)/clay nanocomposites with high degree of clay delamination. In this method, steam was fed into a twin‐screw extruder (TSE) to reduce the PET molecular weight and to facilitate their diffusion into the gallery spacing of organoclays. Subsequently, the molecular weight (M_W) reduction of the PET matrix due to hydrolysis by water was compensated by solid‐state polymerization (SSP). The effect of the thermodynamic compatibility of PET and organoclays on the exfoliated microstructure of the nanocomposites was also examined by using three different nanoclays. The dispersion of Cloisite 30B (C30B) in PET was found to be better than that of Nanomer I.28E (I28E) and Cloisite Na⁺. The effect of feeding rate and consequently residence time on the properties of PET nanocomposites was also investigated. The results reveal more delamination of organoclay platelets in PET‐C30B nanocomposites processed at low feeding rate compared to those processed at high feeding rate. Enhanced mechanical and barrier properties were observed in PET nanocomposites after SSP compared to the nanocomposites prepared by conventional melt‐mixing. POLYM. ENG. SCI., 54:1723–1736, 2014. © 2013 Society of Plastics Engineers     

Morphology and crystallization behavior of the PP/PET nanocomposites

Nanocomposites containing polypropylene (PP), PET, and montmorillonite were prepared in a twin‐screw extruder. X‐ray diffraction, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, polarized optical microscopy, and differential scanning calorimetry were used to characterize the samples. Intercalated and exfoliated morphology were observed in the nanocomposites. The PET domains usually presented spherical shapes and they were the start point to PP crystallization. The average diameter and number of PET domains was evaluated. The influence of addition of PP‐MA as compatibilizer on PP/PET was investigated. The interconnected morphology was observed in the nanocomposite containing PP‐MA. The clay located predominantly in the interphase and in the PET phase. The crystallization process was monitored and the PET crystallization rate was slower in the nanocomposites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Properties of Waterborne Polyurethane/Clay Nanocomposite Adhesives

A series of waterborne polyurethane (WBPU)/clay nanocomposite dispersions using two different organically modified clays, namely Cloisite 15A and Cloisite 30B, were prepared. It was found that the properties of WBPU/clay nanocomposites were highly dependent on both the clay content and the clay surface characteristic (hydrophilic/hydrophobic). A WBPU/clay nanocomposite dispersion with a higher clay content showed a less negative zeta potential. A lower zeta potential for dispersion with Cloisite 30B compared to Cloisite 15A was observed indicating a higher stability of the dispersion. The tensile strength, Young's modulus and adhesive strength of WBPU/clay nanocomposite containing Cloisite 30B were also higher than those of nanocomposite containing Cloisite 15A. The optimum clay contents, with respect to these properties, for nanocomposites with Cloisite 15A and Cloisite 30B were found to be 2 wt% and 3 wt%, respectively.     

Fire‐retardant poly(ethylene terephthalate) by combination of expandable graphite and layered clays for plastics and textiles

Expandable graphite (EG) and polyethylene terephthalate (PET) were melt blended to develop a new nanocomposite intumescent flame retardant in which the effect of combination of EG with nanoclays would be exploited with sodium and organo‐modified montmorillonites, namely Cloisite^®Na, Cloisite^®10A and Cloisite^®30B. X‐ray diffraction analysis coupled to transmission electron microscopy and rheology shows that PET–EG–clay compounds are characterized by an exfoliated and/or intercalated morphology as a function of the type of clay. Thermal stability of composites is enhanced in nitrogen and air by filler adding as compared with neat PET, while combustion rate is decreased both in the bulk material and in textiles made of fibers spun from the compound. Copyright © 2010 John Wiley & Sons, Ltd.     

Bottle‐to‐bottle recycling of PET via nanostructure formation by melt intercalation in twin screw compounder: Improved thermal,barrier, and microbiological properties

Attempts have been made to modify the properties of the injection processing‐scraped PET (denoted as RPET) via intercalation with different levels of organically modified nanoclay (montmorillonite) by melt blending in a corotating twin screw compounder. The clay platelets dispersion state has been qualitatively correlated with the melt linear viscoelastic as well as tensile and barrier properties of the prepared nanocomposites. Oxygen permeation of the nanocomposite PET films showed significant reduction compared with the pristine PET polymer. All the PET/nanoclay composites exhibited no bacterial growth, with no potentiality to generate acetaldehyde, as measured by GC/Mass analyzer. X‐ray diffractometry and transmission electron microscopy performed on the scraped PET/organoclay nanocomposite samples showed increase in d₀₀₁ spacing of the clay layers and their dispersion throughout the PET matrix. Differential scanning calorimetry analysis showed higher crystallization temperature as well as crystallization enthalpy (ΔH_c) for the nanocomposite samples, compared with the unprocessed virgin PET. The RPET nanocomposite samples composed of 3 and 5% of nanoclay exhibited enhanced melt elastic modulus and pseudosolid‐like behavior at low shear frequencies measured by rheomechanical spectroscopy than the unfilled pristine‐scraped PET, indicating the formation of nanoscopic network structure by the clay platelets, which leads to the development of nanostructured resin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and characterization of epoxy based nanocomposites

Epoxy‐clay nanocomposites were synthesized to examine the effects of the content and type of different clays on the structure and mechanical properties of the nanocomposites. Diglycidyl ether of bisphenol‐A (epoxy) was reinforced by 0.5–11 wt % natural (Cloisite Na⁺) and organically modified (Cloisite 30B) types of montmorillonite. SEM results showed that as the clay content increased, larger agglomerates of clay were present. Nanocomposites with Cloisite 30B exhibited better dispersion and a lower degree of agglomeration than nanocomposites with Cloisite Na⁺. X‐ray results indicated that in nanocomposites with 3 wt % Cloisite 30B, d‐spacing expanded from 18.4 Å (the initial value of the pure clay) to 38.2 Å. The glass transition temperature increased from 73°C, in the unfilled epoxy resin, to 83.5°C in the nanocomposite with 9 wt % Cloisite 30B. The tensile strength exhibited a maximum at 1 wt % modified clay loading. Addition of 0.5 wt % organically modified clay improved the impact strength of the epoxy resin by 137%; in contrast, addition of 0.5 wt % unmodified clay improved the impact strength by 72%. Tensile modulus increased with increasing clay loading in both types of nanocomposites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1081–1086, 2005     

Curing kinetics and mechanical properties of epoxy nanocomposites based on different organoclays

The effect of different organoclays and mixing methods on the cure kinetics and properties of epoxy nanocomposites based on Epon828 and Epicure3046 was studied. The two kinds of organoclay used in this study, both based on natural montmorillonite but differing in intercalant chemistry, were I.30E (Nanomer I.30E—treated with a long‐chain primary amine intercalant) and C.30B (Cloisite 30B—treated with a quaternary ammonium intercalant, less reactive with epoxy than the primary amine). The two mixing processes used to prepare the nanocomposites were (i) a room‐temperature process, in which the clay and epoxy are mixed at room temperature, and (ii) a high‐temperature process, in which the clay and epoxy are mixed at 120°C for 1 h by means of mechanical mixing. The nanocomposites were cured at room temperature and at high temperature. The quality of dispersion and intercalation/exfoliation were analyzed by scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction. The heat evolution of the epoxy resin formulation and its nanocomposite systems was measured using differential scanning calorimetry at different heating rates of 2.5, 5, 10, 15, and 20°C min^?1. The cure kinetics of these systems was modeled by means of different approaches. Kissinger and isoconversional models were used to calculate the kinetics parameters while the Avrami model was utilized to compare the cure behavior of the epoxy systems. The cure kinetics and mechanical properties were found to be influenced by the presence of nanoclay, by the type of intercalant, and by the mixing method. POLYM. ENG. SCI., 47:649–661, 2007. © 2007 Society of Plastics Engineers.     

Synthesis and properties of castor oil-based waterborne polyurethane cloisite 30B nanocomposite coatings

Waterborne polyurethane dispersions (WPUDs) were synthesized successfully from castor oil-based polyol, isophorone diisocyanate and dimethylol propionic acid with NCO/OH ratio of 1.5. Different weight percentages of cloisite 30B (1, 2, and 3 wt%) were loaded with WPUDs to prepare nanocomposite films. Prepared prepolymer and nanocomposite films were characterized using FTIR, XRD, SEM, TEM, DSC, and TGA techniques, and coating properties, such as pencil hardness, abrasion resistance, impact resistance, and contact angle, were evaluated. The results obtained from different amounts of clay loading were compared with the pristine castor oil-based WPUDs. The FTIR spectra deconvolution technique was used to study the hydrogen bonding effect within the polymer with an increase in clay content. TGA analysis showed that the thermal stability of WPUDs increases with cloisite 30B (C30B) content. The surface morphology and hydrophilicity/hydrophobicity nature of the nanocomposite films were characterized using scanning electron microscopy and contact angle measurement. The results obtained from tensile tests indicated that the mechanical property of the dispersion system improved with C30B content. A high-performance castor oil-based nanocomposite coating with low volatile organic component can be targeted as an outcome of this work.     

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     

Microstructure and properties of poly(ethylene terephthalate)/organoclay nanocomposites prepared by water‐assisted extrusion: Effect of organoclay concentration

Poly(ethylene terephthalate) (PET)/Cloisite 30B (C30B) nanocomposites containing different concentrations of the organoclay were prepared using two different twin‐screw extrusion processes: conventional melt mixing and water‐assisted melt mixing. The reduction of the molecular weight of the PET matrix, caused by hydrolysis during the water‐assisted extrusion, was compensated by subsequent solid‐state polymerization (SSP). X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses showed intercalated/exfoliated morphology in all PET/C30B nanocomposites, with a higher degree of intercalation and delamination for the water‐assisted process. Rheological, thermal, mechanical, and gas barrier properties of the PET nanocomposites were also studied. Enhanced mechanical and barrier properties were obtained in PET‐C30B nanocomposites compared to the neat PET. The nanocomposites exhibited higher tensile modulus and lower oxygen permeability after SSP. The elongation at break was significantly higher for SSP nanocomposites than for nanocomposites processed by conventional melt mixing. POLYM. ENG. SCI., 54:1879–1892, 2014. © 2013 Society of Plastics Engineers     

Improving heat ageing and thermal properties of silicone rubber using montmorillonite clay

Heat ageing and thermal stability of a silicone rubber (SR) filled with montmorillonite clay (MMT) was investigated. Three types of rubber nanocomposites were prepared with highly exfoliated Cloisite 30B (SR/C30B), intercalated/exfoliated Cloisite Na⁺ (SR/Na⁺MMT), and highly intercalated Cloisite 20A (SR/C20A). This study showed that the SR/C30B nanocomposite exhibited excellent heat resistance in comparison to the other two nanocomposites and neat SR as revealed by higher retention strength. The thermal stability of the rubber in air was strongly dependent on the clay morphology and increased in the following order: highly intercalated/exfoliated SR/Na⁺MMT < highly intercalated SR/C20A < highly exfoliated SR/C30B. The thermogravimetric analyses of the SR/C30B nanocomposite showed a substantial increase in the final residue in comparison with the neat SR. This indicated a major improvement in the thermal stability of the rubber containing the exfoliated clay, which was also supported by the higher activation energy of decomposition measured for the nanocomposite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41061.     

Characterization of latex-based isotactic polypropylene/clay nanocomposites

Polypropylene/clay nanocomposite (PCN) containing 1 wt% organo-modified clay was prepared by latex technology, previously successfully applied for preparation of carbon nanotubes (CNTs)/polymer composites. The level of dispersion of organoclay and the microstructure of the resulting PCNs were characterized by means of X-ray diffraction analysis, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The obtained results have demonstrated that the latex technique represents a promising method for preparation of PP/clay nanocomposites with good dispersion of exfoliated nanoclay particles. The influence of clay nanoparticles on nonisothermal crystallization of PCN was investigated by DSC. The crystallization onset temperature of the matrix rises for about 5 °C when crystallizing from the quiescent melt. Improved thermal stability of PP/nanoclay was observed as evaluated by TGA. The dynamic mechanical analysis reveals an increase in storage modulus of PP matrix in the nanocomposites for 30% over a temperature range, indicating an increase in the stiffness of the material with the addition of organically modified clay.     

Nanofibrillated cellulose,poly(vinyl alcohol), montmorillonite clay hybrid nanocomposites with superior barrier and thermomechanical properties

Nanocomposites of poly(vinyl alcohol) (PVA), nanofibrillated cellulose (NFC), and montmorillonite (MMT) clay were prepared via solvent casting. In addition to investigating the effect of clay loading, PVA matrices crosslinked with poly(acrylic acid) (PAA) were prepared and compared with linear (noncrosslinked) PVA nanocomposites. ¹³C NMR and infrared spectroscopy confirmed the presence of crosslinks. Scanning electron microscopy revealed effective NFC and MMT clay dispersion throughout the nanocomposites, while X‐ray diffraction highlighted the effectiveness of PAA to encourage clay dispersion. MMT clay provided a barrier against the diffusion of water and oxygen (molecules) through the nanocomposite films. Permeability and adsorption were further reduced by crosslinking, while oxygen barrier properties were remarkably enhanced at elevated relative humidities. Thermal stability of the PVA segments was strengthened by the presence of MMT clay and crosslinks. MMT clay–reinforced PVA and NFC within the films, increasing the Young's modulus, tensile strength, and glass transition temperature. Crosslinking further enhanced the thermomechanical properties by imparting physical restraints on polymer chain segments, providing elasticity, and ductility. The hybrid films were successfully reinforced at elevated humidities, with nanocomposites displaying enhanced storage moduli and near‐complete recovery. POLYM. COMPOS., 35:1117–1131, 2014. © 2013 Society of Plastics Engineers     

A Comparative Study of Polystyrene/Layered Silicate Nanocomposites,Synthesized by Emulsion and Bulk Polymerization Methods

Polystyrene/clay (PS/clay) nanocomposites were synthesized by insitu emulsion and bulk polymerization methods. Sodium montmorillonite (Na-MMT) and two organically modified clays (Cloisite 30B and Cloisite 15A) were employed. The effect of clay swelling method and sonication on the d-spacing of silicate layers was also investigated. The surface morphology of pure PS and PS/clay nanocomposites were comparatively investigated using scanning electron microscopy (SEM). Thermogravimetric analysis (TGA) of PS and PS/clay nanocomposites revealed the improved thermal stability of PS/clay nanocomposites compared to pure PS. Results of optical transparency tests showed the better transparency of nanocomposite films compared to the pure PS film.     

Poly(lactic acid)–layered silicate nanocomposites: The effects of modifier and compatibilizer on the morphology and mechanical properties

Poly(lactic acid) (PLA) based nanocomposites were prepared to investigate the effects of types of nanoclays. Five different organically modified nanoclays (Cloisites^®15A, 25A, and 30B, and Nanofils^®5 and 8) were used. Two rubbery compatibilizers, ethylene‐glycidyl methacrylate (E‐GMA) and ethylene‐butyl acrylate‐maleic anhydride, were used in the nanocomposites as compatibilizer‐impact modifier. The degree of clay dispersion, the chemical compatibility between the polymer matrix and the compatibilizers, and changes in the morphology and mechanical properties of the nanocomposites were investigated. The mechanical properties and the morphological studies showed that the interactions between the different compatibilizers and PLA resulted in different structures and properties; such that the dispersion of clay, droplet size of the compatibilizer, and tensile properties were distinctly dependent on the type of the compatibilizer. Compatibility between C25A, C30B, and E‐GMA resulted in the best level of dispersion, leading to the highest tensile modulus and toughness among the compositions studied. In the mentioned nanocomposites, a network structure was formed owing to the high reactivity of the epoxide group of GMA towards the PLA end groups resulting in high impact toughness. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42553.