Analysis of the modulus of polyamide-6 silicate nanocomposites using moisture controlled variation of the matrix properties

The stiffness of PA6 silicate nanocomposites has been measured for a number of silicate fractions and moisture levels. The matrix modulus was varied experimentally by moisture conditioning, resulting in three different moisture levels. The moduli have been analysed with a Halpin-Tsai composite model. This model was used to calculate the matrix modulus in the nanocomposites based on the crystallinity, the amount of surfactant and the moisture content. The measured modulus of the nanocomposites with different moisture content was used to calculate the effective aspect ratios of the reinforcing particles with the Halpin-Tsai model. The calculated aspect ratio for each nanocomposite is independent on the moisture concentration. This indicates the validity of this composite model to describe nanocomposites, despite the small particle size. The results suggest that changes on the molecular level due to the presence of the silicate layers only have a small influence on the modulus, because the modulus can be explained with a composite model. The reduced efficiency of reinforcement at increasing filler levels can be partially explained by the reduction of the matrix modulus due to surfactant and reduced crystallinity, and partially by the occurrence of small stacks of platelets.     

A comparative study of UV active silane-grafted and ion-exchanged organo-clay for application in photocurable urethane acrylate nano- and micro-composites

A number of urethane acrylate nano- and micro-composites have been developed using both ion exchange and silane grafting chemistry. The organically modified clays which were used contained either methacrylate or acrylate functionalities which were capable of reacting with the acrylate groups in the urethane acrylate matrix. [2-(Acryloyloxy)ethyl]trimethyl-ammonium ion (AOETMA) or [2-(methacryloyloxy)ethyl]trimethylammonium ion (MAOTMA) were exchanged onto montmorillonite (MMT) as shown by an increase in the inter-gallery spacing of the MMT. Silane grafting was undertaken using [3-(acryloxy)propyl]dimethylmethoxysilane (APDMMS) or [3-(methacryloxy)propyl]dimethylmethoxysilane (MAPDMMS) and also showed an increase in inter-gallery spacing. The structures of the resulting urethane acrylate composites were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM) and showed predominantly intercalated structures with some exfoliation (more evident in the silane-grafted systems). Dynamical mechanical thermal analysis (DMTA) showed a more significant increase in effective crosslink density (as measured from the plateau of the rubbery modulus) in the composites containing the reactive clays as compared to the unmodified clay, supporting the concept that the acrylate and methacrylate functionalities of the modified clays had reacted with the matrix. Other thermal and mechanical properties were also evaluated.     

The relationship between nano- and micro-structures and mechanical properties in PMMA-epoxy-nanoclay composites

Epoxy-aided dispersion of nanoclay particles in a glassy polymer, polymethylmethacrylate (PMMA), was studied using melt-blending technique. Organically treated nanoclay particles were dispersed in PMMA using mixtures of aromatic and aliphatic epoxies to yield three-phase composite materials, the mechanical properties of which were evaluated and compared with PMMA-nanoclay, epoxy-nanoclay, and PMMA-epoxy composite systems as function of nano- and micro-dispersed domains of phase separated epoxy and nanoparticles. Wide-angle-X-ray diffraction patterns and transmission electron microscope images revealed that the clay particles were in fully exfoliated state in the three-phase composites provided the ratio of epoxy to clay was 10. However, the dispersion of nanoclay to the scale of individual platelets was not achieved as exfoliated clay particles remained as aggregates inside phase separated epoxy domains of approximately 1 μm in diameter. Nevertheless, the values of tensile and impact strengths showed significant improvement over PMMA and PMMA-clay composites.     

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.     

Structural,rheological, and mechanical properties of PA6/SAN/SEBS ternary blend/organoclay nanocomposites

The aim of this study was to investigate the effect of nanoclay addition on the morphological and mechanical properties of PA6/SAN/SEBS ternary blend. Two different nanoclays with different modifiers and two different mixing sequences were used to investigate the role of thermodynamic and kinetic, respectively, in the nanoclays localization. XRD, SEM, TEM, melt rheology, tensile and Izod impact tests were used to characterize the nanocomposites. Results of characterization of nanocomposites showed that clay localization is a very influential parameter to determine the type of morphology and, consequently, mechanical properties of ternary/clay nanocomposites. It was demonstrated that presence of nanoclay in the matrix results in the increase of stiffness, while localization of nanoclay at the interface improves the toughness and tensile strength. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41969.     

Microstructure and rheological properties of pH-responsive core-shell particles

The microstructure and rheological properties of core-shell pH-responsive microgels consisting of poly(methyl methacrylate) (PMMA) particles grafted with a soft layer of methacrylic acid-ethyl acrylate (MAA-EA) cross-linked with di-allyl phthalate (DAP) were examined using dynamic light scattering and rheological techniques. The validity and limitation of the semi-empirical approach to model charged soft microgel particles developed by our group were tested on this core-shell system. The viscosity data for three different core-shell particles showed excellent agreement with the modified Krieger-Dougherty (K-D) model. Good agreement was also observed when our semi-empirical approach was compared against a theoretical model, which confirmed the validity of the semi-empirical approach to model charged soft particles. In addition, we confirmed that the new scaling law which relates the swelling ratio Q of microgels as a function of neutralization degree, α, average number of monomers between two cross-links, N_x, molar fraction of acidic units, y and concentration of mobile counter-ions, CK⁺ and C⁺Na, represented as (Nx/c₀)(CK⁺+C⁺Na)Q+Q2/3 is proportional to yN_xα. All the core-shell data at varying ionic strength and mobile counter-ions concentrations fall onto a master curve.     

Creep and physical aging behaviour of PA6 nanocomposites

The creep and physical aging behavior of various types of PA6 nanocomposites and unfilled PA6 are described. After annealing far above T_g the samples were quenched to room temperature and tested after various ageing times. The creep compliance shows a significant reduction with the addition of exfoliated layered silicate to the matrix polymer. The shape of the creep curves of the nanocomposites is similar to unfilled PA6 and time—ageing time superposition is possible with all materials. The shift rate for superposition is in the same range, but slightly higher in nanocomposites. The creep behavior of nanocomposites conditioned with an equilibrium amount of moisture and dry samples at elevated temperatures shows that the effect of nanofillers is much stronger under these conditions.     

Synthesis and rheological properties of oligoimide/montmorillonite nanocomposites

We report a facile strategy for preparing polyimides (PI)/montmorillonite (MMT) nanocomposites at moderate temperatures that avoids thermal degradation of organically-modified MMT (organo-MMT) that is commonly observed during conventional melt-blending of organo-MMT with commercial high molecular weight PI at elevated temperatures. Novel polyimides of low molecular weight (oligoimides) based on 1,3-bis(3′,4,-dicarboxyphenoxy)benzene and 4,4′ bis(4″-aminophenoxy)diphenylsulfone were synthesized and subsequently melt-blended at temperatures ranging from 150 to 250 °C with special organically-modified montmorillonite clay nanoparticles to form new polyimide/organo-MMT nanocomposites with special combination of physical and chemical properties for diverse applications such as microelectronic components where chemical inertness, high temperature stability, low dielectric constant, mechanical toughness and processability are primary requirements. It was found that application of a strong shearing flow near the glass transition temperature of the oligoimide to the oligoimide/organo-MMT nanocomposite melt blend containing 6±2 vol% of the organo-MMT resulted in three orders of magnitude increase in the viscosity. Partial exfoliation of the organo-MMT together with constrained deformation of the polymer between the rigid nanoparticle layers (as evidenced by formation of the network structure or fractal gel) are thought to be responsible for this observed viscosity behavior. The viscosity behavior is typical for model xylene/MMT system where the MMT particles were dispersed in xylene solvent homogeneously via ultrasonic mixing. This study suggests that the rheological methods used here may provide a valuable analytical tool to accelerate efforts to develop useful polyimide nanocomposites from synthetic oligoimides containing ceramic nanoparticles having different shapes and sizes. Further, because of their facile synthesis and desirable characteristics these polyimide/MMT clay nanocomposites are expected to be excellent model systems for exploring feasibility of new routes for driving organic polymers to self-assemble into useful nanocomposites.     

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.     

Mechanical,chemical, thermal,and rheological properties of recycled PA6/ABS binary and PA6/PA66/ABS ternary blends

The effects of multiple injection molding cycles on the chemical and mechanical properties of PA6/ABS and PA6/PA66/ABS blends are investigated. The chemical structures of both PA6/ABS binary and PA6/PA66/ABS ternary blends do not alter after recycling process. For PA6/ABS binary blend, it is found that the tensile strength, strain at break, elastic modulus, impact strength, flexural strength, and modulus of recycled blend decrease by 6.49%, 15.19%, 21.00%, 9.41%, 7.09%, and 8.25%, respectively, while MFI increases by 23.59% as compared with the virgin blend. After five recycling process for PA6/PA66/ABS ternary blend, the tensile strength, strain at break, and impact strength of recycled blend decrease by 18.00%, 50.80%, and 87.27%, respectively. However, flexural strength and modulus of PA6/PA66/ABS blend increase slightly. For virgin PA6/PA66/ABS blend, MFI value was 7.7 g/10 min and with recycling this value showed an important increase to 31.56 g/10 min after five cycles. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40810.     

Preparation and mechanical properties of exfoliated mica-polyamide 6 nanocomposites using sericite mica

A new mica/polyamide 6 (PA6) nanocomposite was formed by exfoliation of a mica, potassium sericite (K⁺-SE). The powder sample was separated through an air-classifier into D₅₀:6.0 μm (median particle diameter), D₁₀:3.5 μm, and D₉₀:9.5 μm. The K⁺-SE was modified with a dodecylammonium salt (DDA) by ion exchange at 70 °C for four days. The resulting organically modified SE was melt-kneaded with PA6 in a twin-screw kneader at 260 °C. In order to characterize the nanocomposite morphology, X-ray diffraction and transmission electron microscopy were used. Differential scanning calorimetry and mechanical property measurements were also carried out. The morphology of the nanocomposite revealed mica nanolayers with very high aspect ratios; that is, at levels about two times greater than that of conventional exfoliated clay-polymer nanocomposites. A small amount of organically modified SE with 2.1 mass% silicate was sufficient to improve the flexural properties and heat distortion temperature of the nanocomposite. However, overall mechanical properties were not completely improved, because the shearing stress induced during exfoliation of the silicate layers resulted in inhomogenous dispersion of silicate platelets in the matrix. The present study indicates that three factors, degree of exfoliation, aspect ratio and dispersion homogeneity of silicate platelets, play an important role for the development of high performance nanocomposites.     

Relationship between structure and dynamic mechanical properties of a carbon nanofiber reinforced elastomeric nanocomposite

The tensile and dynamic mechanical properties of a nanocomposite, containing modified carbon nanofibers (MCNFs) homogenously dispersed in an elastomeric ethylene/propylene (EP) copolymer semicrystalline matrix (84.3 wt% P), have been correlated with the structure development. These properties were characterized by in situ synchrotron X-ray diffraction during stretching, dynamic mechanical analysis and X-ray analysis techniques over a wide temperature range. Upon sequential drawing, the tensile strength of the nanocomposite film was notably higher than that of the unfilled polymer even though both samples exhibited a similar amount of crystal fraction and the same degree of crystal orientation, revealing the effect of nanofiller reinforcement in the semicrystalline matrix. The mechanical spectra of the 10 wt% MCNF filled samples in both stretched and non-stretched states showed broadening of the elastic modulus at high temperatures, where the corresponding crystallinity index also decreased. It is conceivable that a significant fraction of chain orientation is induced in the vicinity of the nanofillers during stretching, and these stretched chains with reduced mobility significantly enhance the thermal mechanical properties.     

Microstructural and mechanical characteristics of hybrid SiC/Cu composites with nano- and micro-sized SiC particles

Hybrid Cu-SiC composites have been highly considered in order to achieve a combination of electrical and thermal properties along with high strength and wear resistance. However, limited investigations have ever been conducted over the effects of using hybrid (combination of nano and micro size) particles on the wear resistance behavior of these composites. Hence, in the present study, Cu-SiC nanocomposite with 4?vol% nanosize and 4?vol% microsize SiC, and Cu-SiC microcomposite with 8?vol% micro- SiC were fabricated through mechanical milling and hot pressing process. Results revealed the homogeneous dispersion of SiC particles in the matrix, high densification, and ultrafine-grain matrix for the samples. The hybrid nanocomposite showed higher wear resistance, lower friction coefficient and enhanced compressive strength in comparison to the microcomposite. The presence of hybrid particles caused a significant decrease of 61% in the matrix grain size, 53% decrease in the width of wear track, and 35% increase in the compressive strength compared to the nanostructured Cu sample. Investigation of the worn surfaces showed that delamination is the predominant wear mechanism in the Cu-SiC composites. Using hybrid SiC led to decreasing the formation of cracks and pits, and plastic deformation in the worn surfaces.     

Dispersion and rheological properties of concentrated silicon aqueous suspension

This work focuses on the optimization of the rheological properties of silicon suspensions by changing the concentration of a dispersant and the pH value of the dispersing medium. The zeta potential and rheological properties of silicon suspensions as a function of tetramethyl ammonium hydroxide (TMAH) concentration were carried out. The results show that the isoelectric point of the silicon particles was at pH 1.6. A silicon suspension with 46 vol.% particles displayed a minimum viscosity at pH 9.6. The results also show that TMAH is an efficient dispersant by enhancing the absolute value of the zeta potential of silicon particles. The optimum dosage of the dispersant was 0.4 wt.% of silicon particles.     

Correlations between rheological and mechanical properties of mineral filled polypropylene compounds

A comparative study of rheological and mechanical properties of Polypropylene compounds with talc as a mineral filler is presented. It turns out that the main factors determining the mechanical behavior, namely (a) filler concentration, (b) filler particle size, and (c) degree of dispersion, influence the linear viscoelastic properties as well. Thus, a quick method for estimating compound properties from melt rheology is established. © 1994 John Wiley & Sons, Inc.     

RETRACTED ARTICLE: A correlation between the optical and mechanical properties of novel polysilane/polysiloxane nanocomposites

Poly(di-n-hexyl)silanes (PDNHS), which are σ-conjugated conductive polymers were synthesized by the conventional Wurtz-type coupling reaction. PDNHS were incorporated into polymer networks obtained by cross-linking vinyl terminated poly(dimethyl)siloxanes and methylhydrosiloxane-dimethylsiloxane copolymers. From the UV spectra of polysilane/polysiloxane composites, it can be derived that direct correlations exist between the structure of the polysiloxane matrix and the conformation of small amounts of added polysilanes. The degree of cross-linking plays an important role to understand the structure of the polysiloxane matrix. In addition, rheological measurements indicate that the mechanical properties and the degree of cross-linking in the PDNHS/polysiloxane composites are directly correlated. This implies that the optical properties of small amounts of added PDNHS can be correlated to the mechanical properties of the surrounding polymer matrix. Furthermore, this correlation confirms that PDNHS are suitable to probe the properties of complex polymeric structures.     

PP/PA6共混物的形态和流变性能

将聚丙烯（PP）和聚酰胺6（PA6）共混可以使PP和PA6在性能上互补，所得共混物性价比很高。本文分析了PP／PA6共混物在共混时相容性和流变，性对其形态的影响。列举了目前PP／PA6增容剂的研究情况，二相相容时的简单动力学模型，以及分散相PA的含量、增容剂的种类、双螺杆挤出机熔融段的螺杆结构、螺杆转速、共混方式等影响PP／PA6共混物形态的因素。     

FT-IR spectroscopic study of hydrogen bonding in PA6/clay nanocomposites

Fourier transform infrared spectroscopy was used to investigate PA6/clay nanocomposites (PA6CN) with various cooling histories from the melt, including rapid cooling (water-quenched), middle-rate cooling (air-cooling) and slow cooling (mold-cooling). In contrast to pure PA6 dominated by the α-phase, the addition of clay silicate layers favor the formation of the γ-crystalline phase in PA6CN.We focus on the reason why silicate layers favor the formation of γ-phase in PA6. Vaia et al. suggested that the addition of clay layers forces the amide groups of PA6 out of the plane formed by the chains. This results in conformational changes of the chains, which limits the formation of H-bonded sheets so that the γ-phase is favored. If this assumption is correct, PA6CN is expected to show some differences as compared with PA6 with respect to hydrogen bonding.The silicate layers were indeed found to weaken the hydrogen bonding both in the α- and γ-phases. This was also confirmed by X-ray diffraction studies. The γ-phase is most likely concentrated in regions close to the silicate layers, whereas the α-phase is favored in the bulk matrix.     

改性多壁碳纳米管／PA6纤维的制备及力学性能

将多壁碳纳米管(MWNT)氧化后,酰氯化处理,在氨基封端的PA6聚合时加入,制备PA6／MWNT母粒,将母粒同PA6切片熔融共混纺丝,制备PA6／MWNT纤维。用INSTRON 1122型万能材料试验机测定纤维的力学性能。结果表明,改性MWNT的加入提高了PA6纤维的断裂强度,纤维中MWNT质量分数仅为0．05％时,纤维的断裂强度和初始模量最大,分别增加了60％和86％。用扫描电镜观察复合纤维的结构,发现MWNT均匀地分布在PA6中,并与PA6基体间有相互作用,沿纤维轴向取向。     

PA 6/EPDM-g-MAH/HDPE三元共混物的形态与力学性能

制备了聚酰胺(PA)6/马来酸酐(MAH)接枝三元乙丙橡胶(EPDM)(EPDM-g-MAH)/高密度聚乙烯(HDPE)三元共混物,采用扫描电子显微镜观察了三元共混物的相形态,研究了注塑过程的二次剪切流动对该三元共混物相形态的影响,以及三元共混物相形态对其力学性能的影响。结果表明:二次剪切流动有利于PA 6/EPDM-g-MAH/HDPE体系向热力学最稳定的壳核结构发生转变。与PA 6/EPDM-g-MAH二元共混物相比,该三元共混物的力学性能得到较大改善,w(EPDM-g-MAH)为15%时,其Izod缺口冲击强度达85.83 kJ/m2,是纯PA 6的9倍,是同等橡胶含量的PA 6/EPDM-g-MAH二元共混物的2倍。