Moisture absorption in polyamide-6 silicate nanocomposites and its influence on the mechanical properties

The influence of the amount of silicate and the amount of absorbed moisture on the mechanical properties of PA6 nanocomposites is discussed. Diffusion coefficients have been determined from moisture absorption experiments and similar amounts of water were absorbed by nanocomposites with different silicate concentrations. The modulus of the nanocomposites increases with increasing amount of silicate and decreases with increasing amount of absorbed moisture. However, the ductility of the nanocomposites decreases with increasing amount of silicate and increases with increasing moisture content. A more hydrophobic modification of the particles results in a reduction of the degree of exfoliation in PA6, and consequently in a lower modulus, higher ductility and an increased diffusion coefficient compared to particles that are better exfoliated. PA6 nanocomposites can compensate for the decrease of the modulus of PA6 when water is absorbed from the environment.     

Preparation and properties of polyamide-6-boehmite nanocomposites

Colloidal boehmite particles have been included into a polyamide-6 matrix by in situ polymerization. The particles have been used without any surface modification. Characterization of the nanocomposites has been carried out using transmission electron microscopy (TEM), dynamical mechanical analysis (DMA) and differential scanning calorimetry (DSC). TEM images indicate that the particles have been homogeneously dispersed in the polymer. DSC results show that the presence of boehmite affects the form of crystallization of polyamide-6, in which case formation of γ-structure is favored over the α-structure and an additional α′-phase is formed. Some mechanical reinforcement of the matrix has been accomplished as indicated by DMA results. The modulus level off at high boehmite concentrations can be explained by the reduction of the crystallinity, which cancels the effect of the filler.     

The effect of clay on the thermal degradation of polyamide 6 in polyamide 6/clay nanocomposites

The degradation pathway of polyamide 6/clay nanocomposites was studied as a function of clay content. Well-dispersed polymer-clay nanocomposites can be easily obtained by simple melt blending between organically-modified clays and polyamide 6. Polyamide 6-clay nanocomposites exhibit a large reduction in the peak heat release rate, 60%, measured by cone calorimetry. There are no significant differences in the evolved products during thermal degradation of polyamide 6 and polyamide 6/clay nanocomposites in terms of composition and functionality. The main degradation pathway of polyamide 6 is aminolysis and/or acidolysis, primarily through an intra-chain reaction, producing ε-carprolactam, which is the monomer of polyamide 6. As the clay loading is increased, the relative quantity of ε-carprolactam in the evolved products decreases and the viscosity of the soluble solid residues increases. It is thought that inter-chain reactions become significant in the presence of clay because the degrading polymer chains are trapped in the gallery space of the clay during thermal degradation.     

Morphology and mechanical properties of glass fiber reinforced Nylon 6 nanocomposites

Nylon 6 composites containing both an organoclay and glass fibers as fillers were prepared by melt processing. The aspect ratios of the glass fibers and the clay platelets were determined by electron microscopy techniques. The aspect ratio of each type of filler decreased as filler loading increased. A two particle population model for the tensile modulus was constructed based on the Mori-Tanaka composite theory. The experimental levels of reinforcement appear to be reasonably consistent with model predictions when changes in particle aspect ratios are accounted for. The tensile strength increases and elongation at break decreases as the content of either filler increases according to expected trends. Izod impact strength increased with glass fiber content but decreased with clay content.     

A comparison of the temperature dependence of the modulus, yield stress and ductility of nanocomposites based on high and low MW PA6 and PA66

Nanocomposites with both organically modified and unmodified silicate have been prepared by an extrusion process using low and high molecular weight grades of PA6 and a low MW grade of PA66. Mechanical properties have been tested at temperatures ranging from 20 to 120 °C. The modulus increase in all nanocomposites with organically modified nanocomposites is similar: at room temperature an increase in the modulus of approximately 10% for each wt% of silicate is found. PA66 nanocomposites display an identical normalized modulus increase as PA6 nanocomposites, while unmodified silicate nanocomposites show a smaller increase in the modulus. The yield stress also increases with the addition of layered silicate. Low MW PA6 and PA66 nanocomposites show brittle fracture behaviour at room temperature, while high MW PA6 nanocomposites are ductile. With increasing temperature all nanocomposites become ductile at a certain temperature.     

Rubber toughening of nylon 6 nanocomposites

The rubber toughening of nylon 6 nanocomposites prepared from an organoclay was examined as a means of balancing stiffness/strength versus toughness/ductility. Nine different formulations varying in montmorillonite, or MMT, and maleated ethylene/propylene rubber or EPR-g-MA rubber content were made by mixing of nylon 6 and organoclay in a twin screw extruder and then blending the nanocomposites with the rubber in a single screw extruder. In this sequence, the MMT platelets were efficiently dispersed in the nylon 6 matrix. The MMT platelets did not penetrate into the rubber phase. The addition of clay affected the dispersion of the rubber phase resulting in larger and more elongated rubber particles. The tensile properties and impact strength of these toughened nanocomposites are discussed in terms of the MMT and rubber contents and morphology. There is a clear trade-off between stiffness/strength versus toughness/ductility.     

Effects of clay on phase morphology and mechanical properties in polyamide 6/EPDM-g-MA/organoclay ternary nanocomposites

In this study, both organoclay and EPDM-g-MA rubber were used to simultaneously improve the toughness and stiffness of polyamide 6 (PA6). We first prepared PA6/EPDM-g-MA/organoclay ternary nanocomposites using melt blending. Then the composites were subjected to traditional injection molding and so-called dynamic packing injection molding. The dispersion of clay, phase morphology, crystallinity and orientation of PA6 as well the mechanical properties were characterized by WAXD, SEM, DSC, 2D-WAXS and mechanical testing, respectively. The effects of clay on phase morphology and mechanical properties of PA6/EPDM-g-MA blends could be summarized as follows: (1) weakening interphase adhesion between PA6 and EPDM-g-MA rubber particles, resulted in increasing of rubber particle size, as the clay and rubber contents are low; (2) preventing coalescence of rubber domains, arisen in decreasing of rubber particle size, as the clay and rubber contents are high; (3) the blocking effect on the overlap of stress volume around rubber particles caused broadening of the brittle-ductile transition region and decrease of toughness, and (4) the effective stress transfer leading a better reinforcement when the interparticle distance is smaller than the critical value.     

Chemorheology and properties of epoxy/layered silicate nanocomposites

The effect of the organoclay nanoparticles on the rheology and development of the morphology and properties for epoxy/organoclay nanocomposites has been studied. The interlayer spacing increases with the temperature of cure resulting in intercalated morphologies with varying degrees of interlayer expansion, depending on the cure temperature used. Rheological studies of the curing process indicate that intergallery diffusion before curing is essential for exfoliation, before the morphology is frozen in by gelation and vitrification. The maximum increase in modulus was observed for the 2 wt% clay loading. Viscoelastic behavior and mechanical properties of the cured samples were correlated with the morphological and rheological study.     

Compatibilizing effect of maleated polypropylene on the mechanical properties and morphology of injection molded polyamide 6/polypropylene/organoclay nanocomposites

Polyamide 6/polypropylene (PA6/PP=70/30 parts) blends containing 4 phr (parts per hundred resin) of organophilic modified montmorillonite (organoclay) were prepared using twin screw extruder followed by injection molding. Maleated polypropylene (MAH-g-PP) was used to compatibilize the blend system. The mechanical properties of PA6/PP nanocomposites were studied through tensile and flexural tests. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to assess the fracture surface morphology and the dispersion of the organoclay, respectively. X-ray diffraction (XRD) was used to characterize the formation of nanocomposites. The thermal properties were characterized by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The dynamic mechanical properties of PA6/PP nanocomposites were analyzed by using dynamic mechanical thermal analyzer (DMTA). The strength and stiffness of PA6/PP nanocomposites were improved significantly in the presence of MAH-g-PP. This has been attributed to the synergistic effect of organoclay and MAH-g-PP. The MAH-g-PP compatibilized PA6/PP nanocomposites showed a homogeneous morphology supporting the compatibility improvement between PA6, PP and organoclay. TEM and XRD results revealed the formation of nanocomposites as the organoclay was intercalated and exfoliated. A possible chemical interaction between PA6, PP, organophilic modified montmorillonite and MAH-g-PP was proposed based on the experimental work.     

Effect of sample thickness on the mechanical properties of injection-molded polyamide-6 and polyamide-6 clay nanocomposites

The effect of the thickness on the mechanical properties of injection-molded specimens of pure polyamide-6 (PA6) and polyamide-6 clay nanocomposites (PA6-NC) with 5 wt% of layered silicates was investigated. Plates of 0.5, 0.75, 1 and 2 mm thickness were characterized in the injection direction using Dynamic Mechanical Analysis under torsion and tension respectively, and tensile tests. The fracture surfaces were analyzed by Scanning Electron Microscopy. In contrast with PA6, PA6-NC showed thickness effect and clear differences in the mechanical and thermomechanical properties between skin and core, especially in the 2 mm thick samples. Increasing thickness in PA6-NC led to a reduction of tensile modulus and yield stress. In the fracture surface of the thicker tensile specimens the formation of a sheet-like structure was observed. Multiple voiding in the core causing initial failure in this region and a stiffer skin with a better orientation of the layered silicates in the injection direction are two important elements of a micromechanical model proposed in this paper to explain the fracture mechanism in PA6-NC.     

Influence of organo-montomorillonite on mechanical and rheological properties of polyamide nanocomposites

The effect of organically modified montmorillonite (OMMT) on polyamide nanocomposites was studied. OMMT/polyamide nanocomposites were prepared through direct melt compounding on a conventional twin screw extruder. With increasing the loading of OMMT, the Young modulus, elongation at break and tensile strength increased. 1 mass% loading of OMMT/polyamide resulted in 11% increase of the elongation at break compared to virgin polymer, while 4% loading showed 13%. Rheological data like torque, fusion time, viscosity and shear rate were also recorded on Brabender Plasticorder and were correlated with M = CS^a and τ = K(γ)ⁿ. The value n < 1 indicated pseudo-plastic nature of the polyamide/OMMT. The torque decreased with increased loading due to soft nature of OMMT, which acts as a lubricating agent. This improvement in mechanical properties with increase in amount of OMMT loading was also indicated by the reduction in shear viscosity and torque.     

聚丙烯基纳米复合材料的制备方法与力学性能

综述了聚丙烯(PP)基纳米复合材料的制备方法和力学性能的研究进展，介绍了目前国内外研究的以PP为基体与粘土层状物、无机、金属纳米粒子复合制备的复合材料的表面处理、制备方法与材料力学性能的关系。用传统的表面处理方法可改善纳米粒子的分散性与力学性能，少量纳米粒子可使PP同时获得增强增韧。     

Transport properties of electrically conducting nylon 6/foliated graphite nanocomposites

In this work, we analyze the conductivity data of the nylon 6/FG nanocomposites using the normalized percolation equations and the general effective equation. From the interpretations of the derived results, we demonstrate that the microstructure of the nanocomposites can be readily deduced. Taking several factors into account, it turns out that the tunneling mechanism should be responsible for the observed non-universality of the critical exponents. Experimental evidences show that the existence of the tunneling conduction should be attributed to the particular structure of the prepared materials.     

Investigation of nano-SiO2 impact on mechanical and biocompatibility properties of cyanoacryalate based nanocomposites for dental application

Although cyanoacrylate glues are widely used in medicine, cyanoacrylate-based nanocomposites have been recently suggested for dental restorative/filling applications. In the present research, SiO₂ nanoparticles were used as filler for development of a novel dental nanocomposite base on alkoxy-ethyl-cyanoacrylate. The mechanical properties of nanocomposite samples filled with different levels of nano-sized SiO₂ (wt%) were evaluated and comparisons were made with the neat cyanoacrylate. The hardness and wear behavior of the samples were measured using Vickers hardness and pin-on-disk tester, respectively. The wear mechanism of the samples was also evaluated using scanning electron microscopy (SEM). Furthermore, cell biocompatibility of the samples using MTT and LDH assays as well as inflammatory cytokine expression interleukin-6 (IL-6) from L929 cells was investigated. The results showed that an increase in nano-sized SiO₂ content improves hardness and wear resistance of the cyanoacrylate-based nanocomposites and changes the wear mechanism from adhesive to abrasive. The results of cytotoxicity analysis showed a significant reduction in cell viability and IL-6 produced from the samples-exposed L929 cells compared with untreated control cells. Moreover, increasing the nano SiO₂ powder content caused a decrease in the released formaldehyde.     

Manufacturing and characterization of mechanical,biological and dielectric properties of hydroxyapatite-barium titanate nanocomposite scaffolds

In this research, hydroxyapatite (HA)-based ceramics were produced as suitable ceramic implants for orthopedic applications. To improve the physical, mechanical, electrical and biological properties of pure HA, we developed composite scaffolds of HA-barium titanate (BT) by cold isostatic pressing and sintering. Microstructure, crystal phases, and molecular structure were analyzed by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. Bulk density values were measured using the Archimedes method. The effect of different percentages of BT on cell proliferation, viability, and ALP activity of dental pulp stem cells (DPSCs) was assessed by ProstoBlue assay, Live/Dead staining, and p-NPP assay. The obtained results indicate that the HA-BT scaffolds possess higher compressive strength, toughness, density, and hardness compared with pure HA scaffolds. After immersing the scaffold in SBF solution, more deposited apatite appeared on the HA-BT, which results in rougher surface on this scaffold thanpure HA. Electrical properties of HA in the presence of BT are improved. Based on the results of cell culture experiments, composites containing 40, 50 and 60 %wt of BT have excellent biocompatibility, with the best results occurring for the sample with 50 %wt BT.     

Synthesis and properties of nanocomposites of WO3 and exfoliated g-C3N4

The nanocomposites of WO₃ nanoparticles and exfoliated graphitized C₃N₄ (g-C₃N₄) particles were prepared and their properties were studied. For this purpose, common methods used for characterization of solid samples were completed with dynamic light scattering (DLS) method and photocatalysis, which are suitable for study of aqueous dispersions.The WO₃ nanoparticles of monoclinic structures were prepared by a hydrothermal method from sodium tungstate and g-C₃N₄ particles were prepared by calcination of melamine forming bulk g-C₃N₄, which was further thermally exfoliated. Its specific surface area (SSA) was 115 m² g⁻¹.The nanocomposites were prepared by mixing of WO₃ nanoparticles and g-C₃N₄ structures in aqueous dispersions acidified by hydrochloric acid at pH = 2 followed by their separation and calcination at 450 °C. The real content of WO₃ was determined at 19 wt%, 52 wt% and 63 wt%. It was found by the DLS analysis that the g-C₃N₄ particles were covered by the WO₃ nanoparticles or their agglomerates creating the nanocomposites that were stable in aqueous dispersions even under intensive ultrasonic field. Using transmission electron microscopy (TEM) the average size of the pure WO₃ nanoparticles and those in the nanocomposites was 73 nm and 72 nm, respectively.The formation of heterojunction between both components was investigated by UV–Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photocatalysis and photocurrent measurements. The photocatalytic decomposition of phenol under the LED source of 416 nm identified the formation of Z-scheme heterojunction, which was confirmed by the photocurrents measurements. The photocatalytic activity of the nanocomposites decreased with the increasing content of WO₃, which was explained by shielding of the g-C₃N₄ surface by bigger WO₃ agglomerates. This study also demonstrates a unique combination of various characterization techniques working in solid and liquid phase.     

PA6/PVA共混物的相容性与力学性能研究

制备了聚酰胺6/聚乙烯醇(PA6/PVA)共混物,通过DMA、FTIR、DSC和力学性能测试等方法对共混物进行了表征,利用Hoffman-Weeks方程和Flory熔点下降方程求得了PA6的平衡熔点和两种聚合物的相互作用参数,研究了共混物的相容性和力学性能。结果表明:在氢键的作用下,PA6/PVA共混物具有良好的相容性;PA6与PVA相互作用参数为-0.085,进一步证明了PA6/PVA共混物是热力学相容体系;当PVA含量为50%时,PA6/PVA共混物的相容性和力学性能最佳。     

Preparation and mechanical properties of nitrile butadiene rubber/silicate nanocomposites

Elastomer nanocomposites consisting of nitrile butadiene rubber (NBR) latex and layered silicates are prepared by a modified latex shear blending process aided with ball milling. The mode of dispersion of layered silicates in NBR is partially exfoliated and intercalated when the concentration of layered silicates is below 7.5 wt%, as evidenced by transmission electron microscopy and X-ray diffraction results. The tensile and tear mechanical properties are much higher than that of neat NBR. Specifically, the tensile and tear mechanical properties of the NBR/layered silicates increase by 200 and 60%, respectively. The decomposition temperature of the nanocomposites increases slightly.     

Effects of acid- and diamine-modified MWNTs on the mechanical properties and crystallization behavior of polyamide 6

The acid- and diamine-modified multi-walled carbon nanotubes were characterized by XPS, apparent density test and SEM. Their effects on the mechanical properties and crystallization behavior of polyamide 6 (PA6) were comparatively investigated via SEM, DMA, tensile test and DSC. It was revealed that acid treatment could effectively induce polar oxygen-containing groups on the surface of MWNTs, which was beneficial for MWNTs to combine with polar PA6 matrix. However, the interactions such as the hydrogen bonds among the acid-modified MWNTs caused a compact stacking morphology, resulting in a worse dispersion in PA6 matrix. Further diamine modification on the acid-modified MWNTs could graft diamine molecules onto the surface of MWNTs, which weakened the interactions among the MWNTs and thus resulted in a less compact stacking morphology compared with acid-modified MWNTs. Therefore, a better dispersion and a stronger interfacial adhesion of MWNTs in PA6 matrix could be obtained with diamine-modified MWNTs. The storage modulus, glass transition temperature, yield strength, Young's modulus and crystallization temperature of PA6 were found to be improved significantly by the incorporation of diamine-modified MWNTs.     

Reactively compatibilised polyamide6/ethylene-co-vinyl acetate blends: mechanical properties and morphology

Mechanical properties and morphological studies of compatibilised blends of PA6/EVA-g-MA and PA6/EVA/EVA-g-MA were studied as functions of maleic anhydride content (MA) and dispersed phase (EVA-g-MA) concentrations, respectively at blending composition of 20 wt% dispersed phase (EVA-g-MA or combination of EVA and EVA-g-MA). The maleic anhydride (MA) was varied from 1 to 6 wt% in the PA6/EVA-g-MA blend, whereas MA concentration was fixed at 2 wt% in the ternary compositions with varying level of EVA-g-MA. ATR-IR spectroscopy revealed the formation of in situ copolymer during reactive compatibilisation of PA6 and EVA-g-MA. It was found that notched Izod impact strength of PA6/EVA-g-MA blends increased significantly with MA content in EVA-g-MA. The brittle to tough transition temperature of reactively compatibilised blends was found to be at 23 °C. The impact fractured surface topology reveals extensive deformation in presence of EVA-g-MA whereas; uncompatibilised PA6/EVA blend shows dislodging of EVA domains from the matrix. Tensile strength of the PA6/EVA-g-MA blends increased significantly as compared to PA6/EVA blends. Analysis of the tensile data using predictive theories showed an enhanced interaction of the dispersed phase and the matrix. It is observed from the phase morphological analysis that the average domain size of the PA6/EVA-g-MA blends is found to decrease gradually with increase in MA content of EVA-g-MA. A similar decrease is also found to observe in PA6/EVA/EVA-g-MA blends with increase in EVA-g-MA content, which suggest the coalescence process is slower in presence of EVA-g-MA. An attempt has been made to correlate between impact strength and morphological parameters with regard to the compatibilised system over the uncompatibilised system.