Impact fracture behavior of clay-reinforced polypropylene nanocomposites

The micromechanism of plastic deformation during impact loading of polypropylene-clay nanocomposites is examined and compared with the unreinforced polypropylene under identical conditions of processing to underscore the determining role of clay. The addition of clay to polypropylene increases the impact strength in the temperature range of 0 to +70 °C. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) techniques provided an understanding of the micromechanism of plastic deformation in terms of the response of the polymer matrix, nucleating capability of the reinforcement, crystal structure, percentage crystallinity, lamellae thickness, and particle-matrix interface. The enhancement of toughness on reinforcement of polypropylene with nanoclay is associated with change in the primary mechanism of plastic deformation from crazing and vein-type in neat polypropylene to microvoid-coalescence-fibrillation process in the nanocomposite.     

Synthesis and thermal oxidative degradation of a novel amorphous polyamide/nanoclay nanocomposite

A novel amorphous polyamide/montmorillonite nanocomposite based on poly(hexamethylene isophthalamide) was successfully prepared by melt intercalation. Wide angle X-ray diffraction and transmission electron microscopy showed that organoclay containing quaternary amine surfactant with phenyl groups was delaminated in the polymer matrix, resulting in well-dispersed morphologies even at high montmorillonite content. Thermal oxidation behavior of the polymer nanocomposites was studied by thermogravimetric analysis (TGA), and the chemical evolution in the solid residue was monitored by elemental analysis and Fourier transform infrared spectroscopy (FTIR). TGA results showed that the addition of well-dispersed organoclay resulted in a substantial increase (30 °C) in the onset degradation temperature of the nanocomposites as compared to the homopolymer. Elemental analysis on the solid residue indicated that the presence of nanoclay resulted in char formation with greater thermal stability. FTIR spectra showed that thermal degradation in air occurred via both oxidative and non-oxidative mechanisms simultaneously. In the homopolymer, the oxidative mechanism was more dominant. However, with the addition of well-dispersed organoclay, the non-oxidative pathway became more significant. Hence the presence of delaminated nanoclay layers could effectively retard thermo-oxidative degradation of the amorphous polymer by constraining the polymer chains and slowing down the rate of oxygen diffusion through the nanocomposites, but it was not as effective in hindering the non-oxidative degradation reaction pathway.     

High surface area α-alumina preparation by using urban waste

A new method for preparing high surface area α-alumina from urban waste is proposed. The method consists of the precipitation of a precursor that contains bohemite mixed with a linear polymer and subsequently the thermal decomposition of the precursor by heating in nitrogen and air to 1200 °C. The resulting α-alumina consists of nanocrystals of about 100 nm aggregated into larger particles with relatively high surface area (12 m² g⁻¹) and a significant macropore volume of 0.545 cm³ g. Methods of X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) were used to characterize microstructure of prepared materials. Results of differential thermal analysis, thermogravimetry and emanation thermal analysis characterized the thermal behaviour of α-alumina precursors.     

Polyamide-6,6/in situ silica hybrid nanocomposites by sol-gel technique: synthesis, characterization and properties

The organic-inorganic hybrid nanocomposites comprising of poly(iminohexamethyleneiminoadipoyl), better known as Polyamide-6,6 (abbreviated henceforth as PA66), and silica (SiO₂) were synthesized through sol-gel technique at ambient temperature. The inorganic phase was generated in situ by hydrolysis-condensation of tetraethoxysilane (TEOS) in different concentrations, under acid catalysis, in presence of the organic phase, PA66, dissolved in formic acid. Infrared (IR) spectroscopy was used to monitor the microstructural evolution of the silica phase in the PA66 matrix. Wide angle X-ray scattering (WAXS) studies showed that the crystallinity in PA66 phase decreased with increasing silica content. Atomic force microscopy (AFM) of the nanocomposite films revealed the dispersion of SiO₂ particle with dimensions of <100 nm in the form of network as well as linear structure. X-ray silicon mapping further confirmed the homogeneous dispersion of the silica phase in the bulk of the organic phase. The melting peak temperatures slightly decreased compared to neat PA66, while an improvement in thermal stability by about 20 °C was achieved with hybrid nanocomposite films, as indicated by thermogravimetric analysis (TGA). Dynamic mechanical analysis (DMA) exhibited significant improvement in storage modulus (E′) for the hybrid nanocomposites over the control specimen. An increase in Young's modulus and tensile strength of the hybrid films was also observed with an increase in silica content, indicating significant reinforcement of the matrix in the presence of nanoparticles. Some properties of the in situ prepared PA66-silica nanocomposites were compared with those of conventional composites prepared using precipitated silica as the filler by solution casting from formic acid.     

On significant retention of impact strength in clay-reinforced high-density polyethylene (HDPE) nanocomposites

The mechanical response of clay-reinforced polyethylene nanocomposite is investigated and the behavior compared with the un-reinforced polyethylene under identical conditions of processing. The micromechanism of plastic deformation during impact loading of neat polyethylene and clay-reinforced polyethylene nanocomposite are studied with scanning electron microscopy (SEM). The impact strength of composites is linked to structural studies by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM) and SEM observations. The addition of clay to polyethylene retains adequately high-impact strength in the investigated temperature range of −40 to +70 °C. The micromechanism of deformation is altered from a combination of craze and drawing of fibrils in neat polyethylene to microvoid coalescence-fibrillated process in the nanocomposite. The aspects related to micromechanism of deformation are discussed.     

Influence of montmorillonite layered silicate on plasticized poly(l-lactide) blown films

Plasticized poly(l-lactide) (PLA) montmorillonite layered silicate (MLS) nanocomposites were compounded and blown-film processed using a co-rotating twin screw extruder. PLA was mixed with 10 wt% acetyltriethyl citrate ester plasticizer and 5 wt% of an organically modified montmorillonite at various screw speeds. Wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) determined that the compounded pellets and the blown film PLA/MLS nanocomposites were intercalated. The effect of processing screw speeds on the barrier, thermal, mechanical, and biodegradation properties of the nanocomposites were analyzed and compared to the neat polymer. Nanocomposite films show a 48% improvement in oxygen barrier and a 50% improvement in water vapor barrier in comparison to the neat PLA. The thermogravimetric analysis (TGA) showed an overall 9 °C increase in the decomposition temperature for all of the nanocomposites. Differential scanning calorimetry (DSC) has determined that the glass transition, cold crystallization and melting point temperatures were not significantly influenced by the presence of MLS. Mechanical properties of the nanocomposites showed that the Young's modulus increased by 20% and the ultimate elongation of the nanocomposites were not sacrificed in comparison to the neat samples. Biodegradation rates in soil were slightly greater for the PLA/MLS nanocomposite than the pure PLA. However, none of the PLA pure and nanocomposites achieved significant biodegradation levels after 180 days.     

Chain conformational transformations in syndiotactic polypropylene/layered silicate nanocomposites during mechanical elongation and thermal treatment

Polymer nanocomposites prepared by melt-mixing syndiotactic polypropylene (sPP) with a quaternary modified montmorillonite have been studied with FT-IR and XRD spectroscopic techniques. FT-IR spectroscopic analysis has shown that the addition of the nanoclay results in a higher helical content for the syndiotactic polypropylene matrix. Furthermore, FT-IR spectroscopy showed that the presence of the nanoclay hinders the polymeric chains from achieving the degree of transformation from helical to trans-planar form during the application of mechanical stress compared to the neat sPP case. Accordingly, the sPP nanocomposites show a higher tendency relative to neat sPP to return to the initial helical conformation upon either releasing the applied mechanical tension or upon exposing to heat at 120 °C. Additionally, XRD patterns provided evidence that the use of low concentration of nanoclay (1%) resulted in partially exfoliated nanocomposites, while only intercalated nanostructures were produced at high nanoclay contents (10%). However, the application of stress can improve the degree of exfoliation of an sPP nanocomposite. In addition, linear dichroic infrared measurements which allow the monitoring of the influence of the nanoclay on the orientation of the polymeric chains during the application of stress showed that the trans-planar infrared bands exhibit lower orientation in comparison to the same bands in neat sPP, while the addition of nanoclay has no particular influence on the orientation of the infrared bands that are related to helical conformations. Finally, dynamic mechanical analysis (DMA) verified the enhanced mechanical properties of the sPP nanocomposites relative to neat sPP, whereas differential scanning calorimetry (DSC) depicted a slight increase in the glass transition temperature of the polymeric matrix in these nanocomposites, especially for low clay concentrations.     

Graft copolymers of poly(methyl methacrylate) and polyamide-6 via in situ anionic polymerization of ε-caprolactam and their properties

Graft copolymers of poly(methyl methacrylate) and polyamide-6 (PMMA-g–PA6) were investigated via in situ anionic polymerization of ε-caprolactam, using PMMA precursors with N-carbamated caprolactam pendants (PMMA–CCL) as macroactivators and sodium caprolactamate as catalyst. Three grades of PMMA–CCLs obtained by free radical copolymerization were used for synthesizing the PMMA-g–PA6 copolymers with different PMMA content. The resulting graft copolymer was characterized by Fourier-transform infrared spectroscopy and selective extraction. Scanning electron microscopy is used to clarify the phase morphology of obtained polymer by fracture surface. The thermal property, crystallinity and dimensional stability of graft copolymer were studied using differential scanning calorimetry, X-ray diffraction and water absorption measurement. The results show the T_g of graft copolymer is higher than that of neat PA6, but the onset and peak points of graft copolymer melting point are shifted to lower temperature. The percentage crystallinity and water absorption of PMMA-g–PA6 copolymer decrease with increasing PMMA content, but the crystal structure of PA6 is scarcely affected by the presence of PMMA. Graft copolymers have improved dimensional stabilities relative to neat PA6. Upon the incorporation of 19.9 wt% PMMA into PA6, the water absorption of PMMA-g–PA6 copolymer has been reduced from 4.8 for neat PA6 to 2.1%.     

Zeolite filled polyimide membranes for dehydration of isopropanol through pervaporation process

Six mixed matrix membranes (MMMs) were prepared using zeolites of 4A and ZSM-5 incorporated in polyimide of Matrimid 5218. Effects of filler type on membrane morphology and pervaporation performance of MMMs were investigated using isopropanol dehydration. In addition, effects of operating temperature (30, 40, 50, and 60 °C), feed water concentration (10, 20, 30, and 40 wt.%) and permeate side pressure (0 and 15 torr) on pervaporation performance were studied. Scanning electron microscopy (SEM) analysis showed there were good adhesion between the fillers and the polymer matrix. Zeolite 4A has a better contact with the polymer phase and thereby nearly no void is formed in the MMM structure. Pervaporation were performed based on L16 array of Taguchi method for design of experiments. The results showed that the best separation condition is achieved at temperature, feed water concentration, and permeate pressure of 30 °C, 10 wt.% water and 0 torr, respectively. Selectivities of zeolites 4A and ZSM-5 filled MMMs were calculated as 8991 and 3904 compared with 1276 measured for the neat Matrimid 5218 membrane. Permeation rates of the zeolite 4A and ZSM-5 filled MMMs and the neat polymeric membrane were found to be 0.018, 0.016, and 0.013 kg/m² h, respectively.     

Confined crystallization phenomena in immiscible polymer blends with dispersed micro-and nanometer sized PA6 droplets part 4: polymorphous structure and (meta)-stability of PA6 crystals formed in different temperature regions

The genesis and stability of different PA6 crystalline polymorphs, dispersed as micro- and submicrometer sized droplets inside an amorphous polymer matrix, are discussed over a very broad temperature range. Different PA6 droplet sizes lead to different PA6 crystallization events in a 100 °C wide temperature window that extends down to 85 °C. Static WAXD and DSC experiments on micrometer sized PA6 droplets indicate the formation of a stable γ-crystal phase in the region between 175 and 130 °C. Sub-micrometer sized PA6 droplets only crystallize at 85 °C in the β-phase. Upon heating above the PA6 glass transition, these crystals progressively increase their perfection and ultimately transform into the α-phase around 170 °C.     

On the structure and morphology of polyvinylidene fluoride-nanoclay nanocomposites

Polyvinylidene fluoride (PVDF)-nanoclay nanocomposites were prepared by both solution casting and co-precipitation methods with the nanoclay loading of 1-6 wt%. The structure and morphology of the nanocomposite were investigated by wide angle X-ray diffraction (WAXD), polarized light microscopy and transmission electron microscopy (TEM) techniques. PVDF phase transformation behavior was investigated using differential scanning calorimetry and in situ thermal WAXD. All the three typical nanoclay morphologies, namely, exfoliated, partially intercalated and phase separated morphologies, were observed in the PVDF-nanoclay nanocomposites prepared by different methods. In solution-cast samples, phase separation and intercalation occurred depending upon the organic modifiers while complete exfoliation of the nanoclays was observed in the co-precipitated nanocomposites. Furthermore, unique parallel orientation of the nanoclay layers and polymer film surface was achieved in solution-cast samples. β-form PVDF was observed in all the nanocomposites regardless of the nanoclay morphology and contents. Both crystallization and melting temperatures of PVDF were increased with the addition of nanoclay, possibly due to the formation of the β-form PVDF.     

A degradation study of polyamide 11/vermiculite nanocomposites under accelerated UV test

Accelerated photooxidation under ultraviolet (UV) test of polyamide 11 (PA11) films filled with unmodified vermiculite clay at 5 wt% was investigated up to 600 h. Film samples of ~60‐μm thick were prepared by melt compounding using a cast extruder and exposed to UV light irradiation at λ > 295 nm. Fourier transform infrared (FTIR) spectra indicated similar structural changes occurring in both PA11 and PA11/unmodified vermiculite nanoclay (UVMC) nanocomposite along the photooxidation process, resulting in imides and carboxylic acids as the main carbonyl products. It was however observed that the formation rate of carbonyls in the PA11/UVMC nanocomposite was slower than neat PA11. This behavior is consistent with the yellowing index evolution determined by ultraviolet–visible (UV–vis) spectroscopy. Further, the photooxidation stability of the samples was also evaluated by the onset oxidation temperature determined by differential scanning calorimetry. The results indicated a better stability of the nanocomposite film than neat PA11, corroborating well the data obtained by FTIR and UV–vis techniques. POLYM. ENG. SCI., 59:2449–2457, 2019. © 2019 Society of Plastics Engineers     

PMMA-mesocellular foam silica nanocomposites prepared through batch emulsion polymerization and compression molding

PMMA-mesoporous silica nanocomposites were prepared for the first time through in situ batch emulsion polymerization of methyl methacrylate in the presence of large pore MSU-F silica with a mesocellular foam structure (24.8 nm average cavity size) and subsequent compression molding of the polymer-silica nanoparticle mixtures. For composites containing 5.0 wt % silica, the onset decomposition temperature and the temperature at 10% weight loss for the nanocomposite increased 41 °C and 50 °C, respectively, in comparison to pure PMMA. The glass transition temperature of the nanocomposite increased 9.3 °C, as determined by differential scanning calorimetry. In addition, the storage modulus determined by dynamic mechanical analysis increased 17% and 80% at 50 °C and 100 °C, respectively. Substantial improvements in tensile strength (+50%) and modulus (+72%), were achieve at 10 wt % nanoparticle loading. Composites made by compression molding of physical mixtures of PMMA and MSU-F silica powders provide less improvement in thermal stability, glass transition temperature and mechanical properties in comparison to the composites made through in situ batch emulsion polymerization. Unlike previously reported composites made from nanoclays, the silica composites reported here show improvements in both thermal stability and mechanical reinforcement.     

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.     

Microstructure and crystallography in microcellular injection‐molded polyamide‐6 nanocomposite and neat resin

The effects of adding nanoclay to polyamide‐6 (PA‐6) neat resin, and the effects of processing parameters on cell density and size in microcellular injection‐molded components were investigated. In addition, the crystal sizes, structures, and orientation were analyzed with the use of x‐ray diffraction (XRD) and a polarized optical microscope. The standard ASTM D 638‐02 tensile bars for the analyses were molded according to a fractional four‐factor, three‐level, L9 Taguchi design of experiment (DOE) with varying melt temperature, injection speed, supercritical fluid (SCF) concentration, and shot size. It was found that the presence of montmorillonite (MMT) nanoclay greatly reduced the size of the cells and crystals, but increased their density in comparison with neat resin processed under identical molding conditions. In addition, at the sprue section downstream of the machine nozzle, cell size gradually decreased from the part center toward the skin for both the neat resin and the nanocomposite. It was also found that shot size was the most important processing parameter for both the neat resin and nanocomposite in affecting cell density and size in microcellular injection molding components. Weakly preferred crystal orientations were observed on the surface of microcellular injection‐molded PA‐6/MMT tensile bars. Finally, the addition of nanoclay in PA‐6 neat resin facilitated the formation of γ‐phase crystals in the molded components. Polym. Eng. Sci. 45:52–61, 2005. © 2004 Society of Plastics Engineers.     

Crystallization and thermal behavior of microcellular injection‐molded polyamide‐6 nanocomposites

This article presents the effects of nanoclay and supercritical nitrogen on the crystallization and thermal behavior of microcellular injection‐molded polyamide‐6 (PA6) nanocomposites with 5 and 7.5 wt% nanoclay. Differential scanning calorimetry (DSC), X‐ray diffractometry (XRD), and polarized optical microscopy (POM) were used to characterize the thermal behavior and crystalline structure. The isothermal and nonisothermal crystallization kinetics of neat resin and its corresponding nanocomposite samples were analyzed using the Avrami and Ozawa equations, respectively. The activation energies determined using the Arrhenius equation for isothermal crystallization and the Kissinger equation for nonisothermal crystallization were comparable. The specimen thickness had a significant influence on the nonisothermal crystallization especially at high scanning rates. Nanocomposites with an optimal amount of nanoclay possessed the highest crystallization rate and a higher level of nucleation activity. The nanoclay increased the magnitude of the activation energy but decreased the overall crystallinity. The dissolved SCF did not alter the crystalline structure significantly. In contrast with conventionally injection‐molded solid counterparts, microcellular neat resin parts and microcellular nanocomposite parts were found to have lower crystallinity in the core and higher crystallinity near the skin. POLYM. ENG. SCI., 46:904–918, 2006. © 2006 Society of Plastics Engineers     

Morphological,rheological and thermal studies in melt processed compatibilized PA6/ABS/clay nanocomposites

Multicomponent compatibilized blends of polyamide 6 (PA6) and styrene-butadiene-acrylonitrile (ABS) with co-continuous morphology are among commercial alloys with an interesting combination of properties. To further enhance the properties different amounts of nanoclay were incorporated into these blends through a one step melt mixing process. The effect of nanoclay addition on rheological, thermal stability, crystallization and morphological properties of the nanocomposites were investigated and compared with those of the neat blends. The nanoscale dispersion of the clay layers in the blends were confirmed through X-ray diffraction and transmission electron microscopy methods. Rheological investigation indicated an increased viscosity and melt elasticity for the nanocomposite systems. The viscosity of nanocomposites followed a shear thinning flow behavior and decreased with increasing shear rates. The changes in the rheological properties were accompanied by refinement of the co-continuous morphology. For thermal degradation under N₂ atmosphere, the onset and maximum of degradation temperatures for the nanocomposites were as high as the neat blends, while significant improvement in thermal stability (about 60 °C by 3 wt% clay addition) was observed in the air environment. In addition agglomerated clay particles did not significantly affect thermal stability of the polymer matrix. Non-isothermal crystallization results indicated that the clay layers had a retarding effect on the crystal growth rate and facilitated the formation of α crystalline form. In addition no nucleation effect was observed during the crystallization process due to incorporation of nanoclay into the blends.     

Proton conducting polydimethylsiloxane/zirconium oxide hybrid membranes added with phosphotungstic acid

Inorganic polymer based hybrid membranes consisting of zirconium oxide and polydimethylsiloxane (PDMS) have been synthesized by sol-gel processes. The organic/inorganic polymeric hybrid membranes showed thermal stability and flexibility up to 300 °C. The membrane becomes proton conducting polymer electrolyte when added with 12-phosphotungstic acid (PWA). The conductivity of the membranes was measured in the temperature range from room temperature to 150 °C under saturated humidity and a maximum conductivity of 5×10⁻⁵ S cm⁻¹ was obtained at 150 °C.     

Delamination of organo-modified layered double hydroxides in polyamide 6 by melt processing

Layered double hydroxides (LDH) are a class of readily synthesizable layered crystals that can be used as an alternative to the commonly used silicate crystals for the preparation of polymeric nanocomposites. In this work layered double hydroxide/polyamide 6 nanocomposites (LDH/PA6) were prepared from organo-modified LDH by melt processing. The anionic exchange capacity of LDH was varied in order to investigate its influence on the degree of exfoliation. LDH were dispersed by a twin screw micro-extruder at a variety of processing conditions. The nanocomposites were characterized by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), transmission electron microscopy, dynamic scanning calorimetry, and thermogravimetric analysis. It was found that exfoliated nanocomposites were successfully prepared by melt processing with a low exchange capacity LDH, whereas residue tactoids were observed with a high exchange capacity LDH. Shear, together with the exchange capacity, seems to be the key factor for the delamination in LDH/PA6. No major change in the crystalline phase or in the rate of crystallization was observed in the nanocomposite as compared to the neat polymer. A reduction in the onset of thermal decomposition temperature was observed in PA6/LDH compared to neat PA6, likely due to a nucleophilic attack mechanism. The properties of this nanocomposite system are discussed with connections to the current understanding within the broader nanocomposite field.     

Tungsten carbide (WC) nanopowders synthesized via novel core–shell structured precursors

WC powders with a size in the range of 20–60 nm were prepared through carbothermal reduction of a novel core–shell structured precursor in vacuum. The samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The thermolysis process of the precursor has been investigated by themogravimetric analysis and differential thermal analysis (TG–DSC). The results revealed that the single phase WC nanopowders were synthesized at 980 °C for 1 h. Spectra of XPS indicate that the surface of the specimen mainly consists of W, C and O three species elements only. The effects of experimental parameters and reaction mechanism have been explored. Mainly due to the homogeneous chemical composition of the precursor, the synthesizing temperature was greatly lower than the conventional method.