Dispersed Nanoclay Research Articles

The effects of nanoclay and deformation conditions on the inelastic behavior of thermoplastic polyurethane foams

Abstract Under cyclical loading–unloading compression conditions, flexible thermoplastic polyurethane (TPU)/nanoclay composite foams exhibit inelastic behaviors consisting of stress softening, hysteresis loss, and residual strain. In this research, the inelastic behavior of TPU and TPU/nanoclay composite foams was investigated by incorporating different amounts of nanoclay and maximizing strain deformation conditions. As the maximum compression strain was increased from 20% to 40%–60%, the inelastic behavior of TPU neat resin foams (TPUNR) with the same microcellular structures became more profound. Transmission electron microscopy (TEM) and compression testing results indicated that the nanoclay fillers were dispersed in the cell walls (struts). Fully exfoliated nanoclay increased the material's compression strength from 0.13 MPa for TPUNR foam to 0.16 MPa for TPU/5 wt% nanoclay foam (TPUNC5) and 0.36 MPa for TPU/10 wt% nanoclay foam (TPUNC10). With increasing nanoclay content, the relative hysteresis loss, relative residual strain, and relative stress softening of the TPU/nanoclay composite foams decreased markedly. Cell deformation mechanism analyses revealed that the dispersed nanoclay in the cell walls effectively reinforced the foams and retarded the permanent deformation of the cell walls, thereby reducing the inelastic behavior of the TPU/nanoclay foams. That is, the addition of organically modified nanoclay provided an effective way to tune the inelastic behavior of TPU and TPU/nanoclay composite foams.

Stabilized Dye–Pigment Formulations with Platy and Tubular Nanoclays

AbstractAlumosilicate materials of different morphologies, such as platy and tubule nanoclays, may serve as an efficient, protective encasing for colored organic substances and nanoparticles. The adsorption of dyes onto the nanoclays increases their stability against thermal, oxidative, and acid–base‐induced decomposition. Natural organic dyes form stable composites with clays, thus allowing for “green” technology in production of industrial nanopigments. In the presence of high‐surface‐area alumosilicate materials, semiconductor nanoparticles known as quantum dots are stabilized against agglomeration during their colloid synthesis, resulting in safe colors. The highly dispersed nanoclays such as tubule halloysite can be employed as biocompatible carriers of quantum dots for the dual labeling of living human cells—both for dark‐field and fluorescence imaging. Therefore, complexation of dyes with nanoclays allows for new, stable, and inexpensive color formulations.

Effects of nanoclays on the thermal stability and flame retardancy of microcellular thermoplastic polyurethane nanocomposites

Microcellular nanocomposite foams based on thermoplastic polyurethane (TPU) and organically modified layered clays were prepared via an efficient foaming method, microcellular injection molding (MIM). The morphology of the nanoclays was characterized by X‐ray diffraction (XRD) and transmission electron microscopy. The results revealed that the layered nanoclays in the nanocomposite foams achieved a well dispersed morphology within the cell walls due to the MIM foaming process. Postburn SEM images showed that TPU/NC10 foam (with 10 wt% nanoclay) was able to maintain its foam porosity, original shape, and microcellular structure due to the synergistic effects of its microcellular structure and the fully dispersed nanoclays. Thermal stability and flame resistance were assessed by thermogravimetric analysis (TGA) and microscale combustion calorimetry, respectively. TGA results indicated that the nanocomposite foams had a significant decline in the thermal degradation rate compared to the unfilled TPU/NR foam. The flame resistance tests showed that the heat release capacity (HRC) of TPU/NC10 foams was substantially lower (27% lower) than that of the unfilled TPU/NR foam. The char yield of the TPU/NC10 foam was 19.14%, which was almost 18 times higher than that of the unfilled TPU/NR foam. With the presence of the microcellular structure, the HRC values decreased from 266.8 J/g k for solid TPU/NC10 to 235.5 J/g k for TPU/NC10 foams. This work combines two flame retardant mechanisms—the thermal barrier effect of the nanoclay layers and the microcellular self‐intumescing system—in the nanocomposite foams. Our study also provides substantial motivation to produce novel, environmentally‐benign, and flame‐retardant TPU foam using microcellular injection molding. POLYM. COMPOS., 39:E1429–E1440, 2018. © 2017 Society of Plastics Engineers

Relevance of nanocomposite packaging on the stability of vacuum-packed dry cured ham

In this study effects of a novel high barrier multilayer polyamide film containing dispersed nanoclays (PAN) on the stability of vacuum packed dry-cured ham were investigated during 90days refrigerated storage in comparison with non-modified multilayer polyamide (PA) and a commercial high barrier film. Characteristic bands of the mineral in FT-IR spectra confirmed the presence of nanoclays in PAN, enhancing oxygen transmission barrier properties and UV protection. Packaging in PAN films did not originate significant changes on colour or lipid oxidation during prolonged storage of vacuum-packed dry-cured ham. Larger oxygen transmission rates in PA films caused changes in CIE b* during refrigerated storage. Ham quality was not affected by light exposition during 90days and only curing had a significant benefit on colour and TBARS, being cured samples more stable during storage in all the packages used. Packaging of dry-cured ham in PAN was equivalent to commercial high barrier films.

The effect of nanoclay on the crystallization behavior, microcellular structure, and mechanical properties of thermoplastic polyurethane nanocomposite foams

The effects of nanoclay on the crystallization behavior, microcellular structure, and mechanical properties of thermoplastic polyurethane (TPU)/clay nanocomposite (TPUCN) foams were investigated using differential scanning calorimetry, rheometry, scanning electron microscope, transmission electron microscopy, and X‐ray diffraction. It was found that the nanoclay acted as an effective nucleating agent for both crystal nucleation and cell nucleation. As a result, it significantly enhanced the crystallization behavior of the hard segment (HS) domains in TPU while refining the foamed structure of the microcellular injection molded parts. In particular, the average cell diameter of TPUCN foams decreased from 45 µm for neat TPU to 27 µm for TPUCN5 (5 wt% clay) and 18 µm for TPUCN10 (10 wt% clay). Furthermore, the cell density increased from 0.7 × 107 cell/cm3 for neat TPU to 1.4 × 107 cell/cm3 and 3.1 × 107 cell/cm3 for TPUCN5 and TPUCN10, respectively. In addition, the tensile strength also increased by 56.3% and 89.2% with 5 and 10 wt% clay content, respectively. By controlling the cell nucleation behavior through uniformly dispersed nanoclay, this study demonstrates that it is feasible to produce TPUCN foams via microcellular injection molding with desirable microcellular structures and improved mechanical properties. POLYM. ENG. SCI., 56:319–327, 2016. © 2015 Society of Plastics Engineers

Highly exfoliated eco-friendly thermoplastic starch (TPS)/poly (lactic acid)(PLA)/clay nanocomposites using unmodified nanoclay

Highly exfoliated, biodegradable thermoplastic starch (TPS)/polylactic acid (PLA)/sodium montmorillonite (NaMMT) nanocomposites were prepared by an eco-friendly approach, involving in-situ gelatinization of potato starch in presence of dispersed nanoclay followed by melt mixing with PLA. The morphological analysis revealed that the NaMMT was selectively dispersed into the TPS in a highly delaminated manner. An increase in mechanical as well as thermomechanical properties was evident in the presence of PLA and more influenced in the presence of clay. The water absorption was significantly decreased in the presence of PLA (∼8%) itself and both PLA and clay (∼8–12%) in the nanocomposites. The improved mechanical properties along with its biodegradability might lead to a new green material in the area of packaging.

Mechanical Behavior and Fracture Toughness Evaluation of Multiphase Polymer Nanocomposites Using Impact and J-Integral via Locus Method

Fracture behaviors of fibrillar silicate clay (MMT) filled thermoplastic polyolefin (TPO) containing polypropylene (PP) blended with ethylene-propylene-diene monomer (EPDM) were systematically investigated using impact test method and J-integral by locus method. Drastic increase in impact strength is observed for all developed compositions and generally shows higher value for the selected phases containing dispersed nanoclay in PP matrix. A fracture mechanics approach has been adopted by mode I test, and the effects of specimen geometry have been investigated. Increase in interlaminar fracture energy value, Gc, and J-integral value, Jc, is marked as the crack propagated through the composite; that is, a rising “R-curve” is observed. Toughness measurements revealed that the fracture toughness increased with increasing clay content reaching maximum at 3 wt% of clay than pure PP. Moreover, enhancement of fracture toughness was more remarkable than that of stiffness. The fracture surfaces taken from different specimens were observed for exploring the fracture mechanisms using transmission electron microscopy (TEM) revealed a strong particle-matrix adhesion.

Influence of PA6 nanocomposite films on the stability of vacuum-aged beef loins during storage in modified atmospheres

A masterbatch of polyamide 6 (PA6) containing dispersed nanoclays, was used to fabricate a novel multilayer film for vacuum packed meat. Performance of the nanocomposite was compared to a control PA6 multilayer and a high barrier commercial film. Addition of nanoclays improved oxygen barrier properties, UV-blocking capability and stiffness. Beef loins were vacuum-aged using the three films for 0 7, 14 and 21days at 2°C. After each ageing time, beef steaks were packaged in commercial trays and high oxygen atmosphere and stored at 4°C for 9days. Beef quality parameters and gas content were studied during display time in MAP (1, 3, 6 and 9d). Beef quality parameters were not influenced by the packaging materials used during ageing and the performance of nanocomposites was comparable to high barrier films. Ageing had a positive impact on the stabilization of redness up to day 6 in MAP. Thereafter, oxymyoglobin content and oxidation levels were negatively influenced by ageing.

Aged-look vat dyed cotton with anti-bacterial/anti-fungal properties by treatment with nano clay and enzymes

In this research, nanotechnology as a route to functional finishing of textiles was used along with bio-finishing to enhance the cotton fabrics performance. For this purpose, quaternary modified montmorillonite and common enzymes such as cellulase, laccase and their mixture were applied on vat dyed cotton fabric. Characteristic analysis of the treated samples and the dispersed nano clays in the effluent of the treatment was performed by various analyzing methods. The nano/bio-finishing is believed to impart antibacterial and antifungal activities with simultaneously higher lightness, advanced softness and handle properties into cotton fabrics. Moreover, cotton fabrics were proved to have no adverse effects (low toxicity) on human dermal fibroblasts. Findings suggest the potential of the proposed method in reducing the risk of microorganism for textile applications and imparting better handle and appearance properties.

Thermoplastic polyurethane/clay nanocomposite foam made by batch foaming

In this study, the foaming of nonwoven fabrics and bulk polymers was investigated. Four different polymers that are commonly used for textiles including polyethylene terephthalate, thermoplastic polyurethane, thermoplastic polyether ester elastomer and polypropylene were foamed by batch foaming. Among the polymers, thermoplastic polyurethane seems to be the most promising material since it possesses the highest cell density and smallest cell size. In addition, nanoclay was added to thermoplastic polyurethane to promote cell nucleation and to increase the cell density. The results showed that well dispersed nanoclay in thermoplastic polyurethane served as an excellent nucleation agent and the cell structure was improved. The cell size of thermoplastic polyurethane nanocomposite foam decreased to 1 µm while the cell density increased to 3 × 1011 cells/cm3.

Dielectric Properties of PE/Clay Nanocomposites

Polyethylene/nanoclay specimens containing from 0 to 5% nanoclays were prepared from a commercially available premixed PE/nanoclay masterbatch containing 50% wt of nanoclay. The masterbatch was diluted to the desired concentration by adding PE along with various amounts of compatibilizer in order to achieve the best possible dispersion of the nanoclay platelets. The dielectric response of the compounded samples was investigated using a combination of time and frequency‐domain spectroscopy in order to cover a wide frequency window. Both techniques were in good agreement when the time‐domain data was transformed into frequency‐domain data. Despite their low concentration, the addition of the dispersed nanoclays led to a significant alteration of the material dielectric response in the form of the appearance of various interfacial relaxation processes and an increase of charge carrier transport within the insulation material. Moreover, an onset of nonlinear charge transport process was observed at moderate fields for specimens containing a relatively low level of nanoclays. The high‐field breakdown strength was shown to have been improved by the incorporation of the nanoparticles, particularly when the exfoliation was enhanced by the use of a maleic anhydride grafted polyethylene compatibilizer.

Conductivity and methanol permeability of sulfonated polystyrene membrane with dispersed montmorillonite nanoclay

AbstractSulfonated polystyrene membranes with dispersed montmorillonite (MMT) nanoclay were prepared and their conductivities, methanol permeabilities and other characteristics were presented in this study. Sulfonated polystyrene membranes were recast by employing various solvents such as dimethyl sulfoxide (DMSO), chlorobenzene/n‐butanol, chlorobenzene/DMSO and toluene/n‐butanol. These solvents enhanced the ratio of proton conductivity to methanol permeability (C/P ratio) of sulfonated polystyrene membranes, especially DMSO. To reduce the methanol permeability, surfactant‐modified MMT nanoclay, which has a large surface area, was blended with sulfonated polystyrene. The methanol permeability of the sulfonated polystyrene with dispersed nanoclay is 1/10 the value of Nafion® and the activation energy of methanol permeability is about 28 kJ/mol. As DMSO was used as a solvent, the conductivity over permeability ratio of the membrane with 14.38% sulfonation was double the value of Nafion®. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

The Effect of Gel and Pressure Induced Flow (PIF) Processing Conditions on the Dispersion and Intercalation of MMT Nanoclay in UHMWPE/ Montmorillonite (MMT) Clay Based Nanocomposite Sheets

The preparation of dispersed nanoclay in nanocomposite sheets is reported based on preparation of UHMWPE gel sheet with nanoclay of MMT by using paraffin oil as a solvent, and removing this oil using PIF and extraction processes. The microstructure of gel sheet studied by X-Ray diffraction XRD, transmission electron microscopy (TEM); Scanning electron microscope (SEM); and differential scanning calorimetry (DSC). The obtained results show good dispersion, partially exfoliation and fully intercalation of MMT nano-particle. The MMT nanoparticles take place between the layers of microstructure gel sheet, i.e. MMT onto the layer surface by means of these processes in the misconstrue gel sheet shows that the layers spacing was increased significantly. For intercalated nanocomposites; different layers spacing corresponds to different chain flexibility and the presence of multi-peaks is caused by the processing of these materials. The images obtained by SEM present a gel-like layers structure of UHMWPE/MMT gel sheet as a result of the deformation and re-arrangement of the gel sheets during PIF process.

Stiffening of Polycarbonate by Addition of a Highly Dispersed and Fibrillated Amorphous Polyamide‐Based Nanocomposite

AbstractTernary systems consisting of blends of polycarbonate (PC) from bisphenol A and minority amounts of an amorphous polyamide reinforced with organically modified nanoclay (naPA), were obtained in the melt state. The nanoclay was widely exfoliated inside the dispersed naPA phase. The dispersed phase exhibited a very fine size (up to 0.36 µm), indicating compatibilization. Compatibilization was attributed to interactions between the aPA and the PC. The nanocomposite showed a lower compatibility than their corresponding blends. This lower compatibility of the nanocomposite was attributed to a hindrance of the interaction by the migrated surfactant of the organoclay. The presence of fibrillation in conjunction with a dispersed nanoclay resulted in additive enhancing effects on the modulus and yield stress. This led to modulus increases up to 46% with respect to that of the neat matrix upon the addition of 25% naPA‐10. Besides exhibiting these remarkable modulus values, these systems show an elongation at break similar to that of the neat PC matrix.magnified image

Phenolic matrix nanocomposites based on commercial grade resols: Synthesis and characterization

Polymer Layered Silicate Nanocomposites based on a commercial grade resol were produced using a simple, low labor cost, mechanical approach which allowed to avoid the process of intercalative polymerization of phenol and formaldehyde. Commercial compatibilized montmorillonite was selected as the main nanoreinforcement, while the matrix was a resol diluted in methanol. The aim of this work was to optimize the production technique of the above mentioned nanocomposites. Therefore intercalation of the resin was promoted by high speed mixing, and the processing parameters were varied in order to find the optimum dispersion. The produced nanocomposites were characterized and compared by means of X-ray diffraction, SEM and thermogravimetric analysis. The results of the characterization tests indicated that it was possible to obtain a good degree of dispersion as well as and uniform distribution of the nanoclay platelets. However, TGA measurements showed that the introduction of well dispersed nanoclays did not result in a consistent improvement of thermal stability respect that of the neat resol.

Thermal degradation analysis and XRD characterisation of fibre-forming synthetic polypropylene containing nanoclay

Flammability of synthetic fibres is significantly worse than that of bulk polymers because of the high surface area to volume ratio and the low tolerance to high filler loadings in the fibre production process. Introducing nanocomposite structures has the potential to enhance the char formation at relatively low loadings of nanoparticulate fillers and hence can reduce the flammability of synthetic polymers and fibres. This paper reports thermal degradation analysis results in conjunction with TG analysis under different atmospheres and further studies of X-ray diffraction characterisation of fibre-forming polypropylene containing selected dispersed nanoclays. The concentrations of hydrocarbons, carbon monoxide and carbon dioxide released during the TG analysis have been monitored and analysed by using a combined electrochemical infrared analyser. The intensity changes of the crystallinity peaks and nanoclay peaks in the polymer and composites are discussed.

Improvement of the Mechanical Properties and Creep Resistance of SBS Block Copolymers by Nanoclay Fillers

AbstractSBS nanocomposites based on a SBS triblock copolymer containing different weight fractions of a commercial Cloisite 20A organoclay were prepared by melt‐processing. Extensive electron microscopy as well as WAXS and static tensile and tensile creep tests were used to evaluate the resulting morphological and mechanical properties of the nanocomposites. The nanocomposite morphology is characterized by a combination of intercalated and partly exfoliated clay platelets with occasional clay aggregates present at higher clay contents; nanocomposite features that are reflected by the results of both the static tensile as well as the tensile creep tests at room temperature. For this particular thermoplastic elastomer nanocomposite system, well dispersed nanoclays lead to an enhanced stiffness and ductility; effects that induce promising improvements in nanocomposite creep performance.magnified image

Nanoclay‐Modified Rigid Polyurethane Foam

Montmorillonite‐based organoclay was incorporated into rigid polyurethane foams. Clay was dispersed first in the isocyanate component ultrasonically. The dispersion was investigated using small angle X‐ray scattering and rheology. It was found that using toluene as common solvent enhanced dispersion significantly. The addition of 1 wt% clay resulted in reduced cell size from 0.40 to 0.28 mm and increased cell number density on 300‐index foams. Gas chromatography showed that diffusion of blowing agent out of the closed cells of the foam decreased by more than 82% with clay loading. The reduction in permeability is caused by the combined effect of smaller cell size and dispersed nanoclay acting as diffusion barrier. At 1% clay no mechanical strength improvements were observed. Higher levels of clay loading caused significant viscosity increase and a yield stress that made mixing the reactive components difficult. Dedicated to Professor John L. Stanford on the occasion of his 60th birthday.

Flammability, degradation and structural characterization of fibre-forming polypropylene containing nanoclay–flame retardant combinations

We have shown previously that the introduction of nanoclays can reduce the flammability of synthetic fibre-forming polymers like polyamides 6 and 6.6 only if used in conjunction with conventional flame retardants. In this work we report initial studies of the effects of dispersed nanoclays with low concentrations of selected flame retardants introduced into polypropylene on flammability, thermal degradation and X-ray diffraction behaviours. Flame retardants used include ammonium polyphosphate as a conventional char-former and a hindered amine stabiliser known to have flame retarding characteristics in polypropylene.