Reinforcement and environmental degradation of nylon-6/clay nanocomposites

Three Dimensional Printing of Multiscale Carbon Fiber-Reinforced Polymer Composites Containing Graphene or Carbon Nanotubes

Three-dimensional printing offers a promising, challenging opportunity to manufacture component parts with ad hoc designed composite materials. In this study, the novelty of the research is the production of multiscale composites by means of a solvent-free process based on melt compounding of acrylonitrile-butadiene-styrene (ABS), with various amounts of microfillers, i.e., milled (M) carbon fibers (CFs) and nanofillers, i.e., carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs). The compounded materials were processed into compression molded sheets and into extruded filaments. The latter were then used to print fused filament fabrication (FFF) specimens. The multiscale addition of the microfillers inside the ABS matrix caused a notable increase in rigidity and a slight increase in strength. However, it also brought about a significant reduction of the strain at break. Importantly, GNPs addition had a good impact on the rigidity of the materials, whereas CNTs favored/improved the composites' electrical conductivity. In particular, the addition of this nanofiller was very effective in improving the electrical conductivity compared to pure ABS and micro composites, even with the lowest CNT content. However, the filament extrusion and FFF process led to the creation of voids within the structure, causing a significant loss of mechanical properties and a slight improvement of the electrical conductivity of the printed multiscale composites. Selective parameters have been presented for the comparison and selection of compositions of multiscale nanocomposites.

Dependence of the Dynamic Mechanical Properties and Structure of Polyurethane-Clay Nanocomposites on the Weight Fraction of Clay

The effect of clay and chemical cross-linking on the dynamic mechanical properties of polyurethane reinforced with different concentrations of organically modified montmorillonite clay is investigated in this study. The polyurethane matrix is constituted of polytetrahydrofuran soft segment and 4,4′-methylenebis(phenyl isocyanate) hard segment. Glycerin was used as the chemical crosslinking agent, while Cloisite 30B clay was the reinforcing filler. The nanocomposites containing up to 1 wt.% clay showed a uniform dispersion of clay; however, the nanocomposites containing higher concentrations of clay showed the presence of heterogeneities. Dynamic mechanical spectroscopy, DMS revealed that the nanocomposites containing between 2 and 10 wt.% clay had two glass transition temperatures, Tg,1 and Tg,2. The higher-temperature glass transition temperature, Tg,2 increased with increasing clay concentration, while the low-temperature glass transition temperature, Tg,1 decreased with increasing clay concentration. The nanocomposites containing low clay concentrations up to 1 wt.% showed only one glass transition temperature with a narrow glass transition region. The crosslink density for the nanocomposites increased with increasing wt.% clay.

Stress Dependency of Creep Response for Glass/Epoxy Composite at Nonlinear and Linear Viscoelastic Behavior

This research is aimed at comparing the stress dependency of creep viscoelastic behavior for glass/epoxy composite and neat epoxy close to the glass transition temperature and room temperature. Long-term creep performance of quasi-unidirectional composites and quasi-isotropic stacking sequence composites is modeled based on the time-stress superposition principle (TSSP). Linearity and nonlinearity of viscoelastic behavior and stress-dependence correlations were investigated for quasi-isotropic stacking sequence composite at 25°C and 50°C (near the glass transition temperature). Stress dependency of creep stages (primary, secondary, and tertiary) of neat epoxy was evaluated at this range of temperature. The prediction results of composite at room temperature show that the raising of the stress levels leads to the acceleration of viscoelastic strain values, but the creep compliance does not present any dependency. Besides, the reduction of viscoelastic ability is realized by measuring less amount of creep compliance at higher stress level in the glass transition temperature. These observations confirmed the linearity and nonlinearity of viscoelastic behavior at room and glass transition temperature, respectively. Similar results of neat epoxy revealed that the increase in the stress level accelerates the strain values at room temperature and decreases the creep resistance at glass transition temperature. Failure morphologies of epoxy sample fractured at room temperature are included scarp, cusp, and river line; however, close to the glass transition temperature, more expansive mirror zones appeared. Fiber architecture significantly affected the secondary stage regime by providing load-bearing ability. Thereby, creep rate reduction and enhancement of creep lifetime and creep resistance would be reported using unidirectional reinforcing in contrast to those of the multilayer sequence one.

An Investigative Study on the Progress of Nanoclay-Reinforced Polymers: Preparation, Properties, and Applications: A Review

Nanoclay-reinforced polymers have attracted considerable universal attention in academic and industrial research due to their outstanding properties and their ever-expanding utilization in diversified applications. In that regard, in the present review, the structure of layered silicate clay, as well as procedures for clay material modification, are outlined. We also discuss the general characterization techniques, synthesis methods, and various properties of polymer-clay nanocomposites (PCNs), and some examples likewise are depicted from the scientific literature. The study's primary goal is to provide an up-to-date survey of polymer-clay nanocomposites and their specific applications in industries such as automotive, flame-retardant, and biomedical applications, coating, and packaging.

Influence of mixing energy on the solid-state behavior and clay fraction threshold of PA12/C30B® nanocomposites

This study focuses on the influence of mixing energy on the solid-state behavior and clay fraction threshold of nanocomposites. Thus, three polyamide12/clay (PA12/C30B®) nanocomposites exhibiting different nanostructures were prepared from three sets of processing conditions. Then, thermal and dynamical viscoelastic properties of these nanocomposites were analyzed, in relationship with the material nanostructure and processing conditions. For the first time, the solid-state properties of the nanocomposites revealed the existence of a critical specific mixing mechanical energy. Below this critical value, an increase of mechanical energy refines the structure, improving some end-use properties of the nanocomposite. Above this value, a high mixing energy supply is necessary in order to significantly modify the structure. They also highlighted that the clay fraction threshold, which is commonly attributed to the formation of a three-dimensional percolated network, decreases with increasing specific mixing energy, less significantly when this energy is superior to its critical value.

The Influence of Nanoclay on the Flame Retardancy and Mechanical Performance of Recycled Carpet Composites

In the present study, we recycled waste carpet using a vacuum-assisted resin transfer molding (VARTM) process. Three different variations of carpet composites were fabricated, namely, neat epoxy, clay-coated, and clay-infused carpet composites. The carpet composite samples were degraded hygrothermally as well as under a cyclic UV condensation condition. Presence of clay was shown to impede the moisture absorption and UV degradation in the carpet composites. Flexural properties also showed that the presence of clay slows the degradation process of the composites. The flame retardancy result indicated that the presence of clay in the polymer network decreases the ignition time of the carpet composites.

Characterizing the nanoclay induced constrained amorphous region in model segmented polyurethane–urea/clay nanocomposites and its implications on gas barrier properties

AFM images of the segmented PU/clay nanocomposite with labeling of various phases.

Using water to modify the localization of clay in immiscible polymer blends

The injection of water during melt blending modified the localization of clay in immiscible polymer blends from one phase to the other and improved their dispersion state.

Vegetable oil derived solvent, and catalyst free "click chemistry" thermoplastic polytriazoles

Azide-alkyne Huisgen “click” chemistry provides new synthetic routes for making thermoplastic polytriazole polymers—without solvent or catalyst. This method was used to polymerize three diester dialkyne monomers with a lipid derived 18 carbon diazide to produce a series of polymers (labelled C18C18, C18C9, and C18C4 based on monomer chain lengths) free of residual solvent and catalyst. Three diester dialkyne monomers were synthesized with ester chain lengths of 4, 9, and 18 carbons from renewable sources. Significant differences in thermal and mechanical properties were observed between C18C9 and the two other polymers. C18C9 presented a lower melting temperature, higher elongation at break, and reduced Young's modulus compared to C18C4 and C18C18. This was due to the “odd-even” effect induced by the number of carbon atoms in the monomers which resulted in orientation of the ester linkages of C18C9 in the same direction, thereby reducing hydrogen bonding. The thermoplastic polytriazoles presented are novel polymers derived from vegetable oil with favourable mechanical and thermal properties suitable for a large range of applications where no residual solvent or catalyst can be tolerated. Their added potential biocompatibility and biodegradability make them ideal for applications in the medical and pharmaceutical industries.

Preparation and characterization of polyhydroxybutyrate/polycaprolactone nanocomposites

Polyhydroxybutyrate (PHB)/polycaprolactone (PCL)/stearate Mg-Al layered double hydroxide (LDH) nanocomposites were prepared via solution casting intercalation method. Coprecipitation method was used to prepare the anionic clay Mg-Al LDH from nitrate salt solution. Modification of nitrate anions by stearate anions between the LDH layers via ion exchange reaction. FTIR spectra showed the presence of carboxylic acid (COOH) group which indicates that stearate anions were successfully intercalated into the Mg-Al LDH. The formation of nanocomposites only involves physical interaction as there are no new functional groups or new bonding formed. X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that the mixtures of nanocomposites are intercalated and exfoliated types. XRD results showed increasing of basal spacing from 8.66 to 32.97 Å in modified stearate Mg-Al LDH, and TEM results revealed that the stearate Mg-Al LDH layers are homogeneously distributed in the PHB/PCL polymer blends matrix. Enhancement in 300% elongation at break and 66% tensile strength in the presence of 1.0 wt % of the stearate Mg-Al LDH as compare with PHB/PCL blends. Scanning electron microscopy (SEM) proved that clay improves compatibility between polymer matrix and the best ratio 80PHB/20PCL/1stearate Mg-Al LDH surface is well dispersed and stretched before it breaks.

Viscoelastic behavior and reinforcement mechanism in rubber nanocomposites in the vicinity of spherical nanoparticles

The viscoelastic behavior and reinforcement mechanism of nano ZnO reinforced natural rubber (NR) nanocomposites were investigated in this study. Dynamic mechanical analysis was performed to investigate the nature of the constrained polymer region in NR-nano ZnO nanocomposites, and the constrained polymer region is responsible for the reinforcement mechanism. The viscoelastic and tensile properties of NR nanocomposites were investigated with respect to the effect of nanofiller loading. All the nanocomposites showed a significant increase in storage modulus in the glassy and rubbery regions, the shift of the tan δ peak to the higher temperature region, and the lowering of the tan δ peak intensity compared to neat NR. The enhancement in the modulus is related to the weight % of the added nano ZnO as well as the volume of the constrained rubber chains in the proximity of ZnO nanoparticles. The study of the constrained volume of the polymer indicates that the structure of the nanocomposite possesses a moderately strong interfacial interaction between rubber chains and ZnO nanoparticles. The type of rubber-nanofiller interaction strongly influences the amount and modulus of the constrained region and contributes to the enhancement in the storage modulus of the resulting nanocomposites. The volume fraction of the constrained region of the NR nanocomposites was found to have good linear correlation with the weight % of nano ZnO. It was also understood that there should exist an optimum cross-linking density for a certain nanofiller reinforced rubber system, as well as partial physical adsorption of macromolecular rubber chains on the nanofiller surface. An optimum nanofiller loading is necessary for moderately strong rubber-nanofiller interaction and hence for the enhancement in the mechanical properties of the NR nanocomposites. A core-shell morphology model and constrained polymer model have been proposed to explain the constrained polymer chains in the NR-nano ZnO nanocomposite system on the basis of these results.

Interaction and structure in polyelectrolyte/clay multilayers: a QCM-D study

This study focuses on the investigation of the influence of the ionic strength on the internal structure, film forming behavior, and swelling properties of polyelectrolyte/clay multilayers. Layer-by-layer films were prepared with three different polyelectrolytes [polyethylenimine (PEI), polydiallyldimethylammoniumchloride (pDADMAC), and 2-hydroxy-3-trimethylammonium propyl chloride starch (HPMA starch)] in combination with laponite clay platelets on three different surfaces. All experiments were carried out at two different ionic strengths (30 mM or 500 mM NaCl). The experiments performed with strong polyelectrolytes revealed a higher film thickness and adsorbed masses of clay and polyelectrolyte at 500 mM NaCl. The films containing PEI showed different behavior and were considerably less sensitive to changes in the ionic strength. This was also reflected by the swelling behavior as demonstrated by quartz crystal microbalance with dissipation (QCM-D) measurements. Films comprising PEI showed, in contrast to the other polyelectrolytes, much lower swelling in water leading to more compact and stable films in humid environments which is important for numerous applications of LbL clay coatings.

Rotational Molding of Polyamide-6 Nanocomposites with Improved Flame Retardancy

The aim of this work was to develop polyamide-6/ organic-modified montmorillonite (omMMT) nanocomposites for the production of hollow parts by rotational molding. Particular emphasis was placed on the mechanical and flame retardancy properties needed for the fabrication of vessels for flammable liquids. The morphology of the melt compounded nanocomposites, produced by melt compounding, was investigated by X-ray diffraction measurements (WAXD), and Transmission Electron Microscopy (TEM) showed an exfoliated structure. Rheological measurements were used in order to verify whether the viscosity of materials was adequate for rotational molding. While thermomechanical analysis has revealed that neat PA6 and its nanocomposites were not suitable for rotational molding, due to the very low thermal stability of the polymer, the addition of a thermal stabilizer, shifted the onset of degradation to higher temperatures, thus widening the processing window of both PA6 and PA6 nanocomposites. Large-scale vessel prototypes were obtained by rotational molding of thermo-stabilized PA6 and its nanocomposites, and samples extracted from the rotomolded parts were characterized with respect to physical and mechanical properties. It was found that the PA6 nanocomposites exhibited significant improvements at cone calorimeter tests in comparison with neat PA6.

Preparation and characterization of nitrile butadiene rubber-nanoclay composites with maleic acid anhydride as compatibilizer. Part I

Nitrile butadiene rubber (NBR)-nanoclay composites have been prepared. Maleic acid anhydride-treated organoclay (MOC) was synthesized and utilized as a compatibilizer. The prepared clay structures were analyzed by Fourier transform infrared (FTIR) spectroscopy. Furthermore, the FTIR investigation confirmed the incorporation of (MOC) in the NBR matrix, X-ray diffraction analysis indicated that an exfoliated structure was obtained, and scanning electron microscope images displayed the good interaction between the MOC and the rubber matrix. The influence of the MOC content (i.e. 1, 3, 5, 10, 20 phr) relative to the micrometer clay (i.e. 10, 20 phr) on the NBR compounds was analyzed through rheometric and swelling characteristics. The rheometric study demonstrated an increase in minimum and maximum torques, delayed scorch time and optimum cure time for the MOC (3 phr)-incorporated NBR compound compared to pure NBR. The cure rate index followed the same trend. In addition, these particular compounds showed decreased equilibrium swelling in toluene solvent, increased crosslinking density, a greater volume fraction and bound rubber content compared to the corresponding rubber filled with micrometer clay.

Polymer nanocomposites: structure, interaction, and functionality

This feature article discusses the main factors determining the properties of polymer nanocomposites with special attention paid to structure and interactions. Usually more complicated structure develops in nanocomposites than in traditional particulate filled polymers, and that is especially valid for composites prepared from plate-like nanofillers. Besides the usually assumed exfoliated/intercalated morphology, i.e. individual platelets and tactoids, such nanocomposites often contain large particles, and a network structure developing at large extent of exfoliation. Aggregation and orientation are the most important structural phenomena in nanotube or nanofiber reinforced composites, and ag-gregation is a major problem also in composites prepared with spherical particles. The surface characteristics of nanofillers and interactions are rarely determined or known; the related problems are discussed in the paper in detail. The surface of these reinforcements is modified practically always. The goal of the modification is to improve dispersion and/or adhesion in nanotube and spherical particle reinforced composites, and to help exfoliation in nanocomposites containing platelets. However, modification decreases surface energy often leading to decreased interaction with the matrix. Very limited information exists about interphase formation and the properties of the interphase in nanocomposites, although they must influence properties considerably. The properties of nanocomposites are usually far from the expectations, the main reason being insufficient homogeneity, undefined structure and improper adhesion. In spite of considerable difficulties nanocomposites have great potentials especially in functional applications. Several nanocomposite products are already used in industrial practice demonstrated by a few examples in the article.