Influence of platelet aspect ratio and orientation on the storage and loss moduli of HDPE-mica composites

Composites of HDPE and glass or mica particles with different aspect ratios and surface modifications were prepared. The aspect ratio of the mica platelets was evaluated by image analysis of SEM micrographs. Test specimens, in which the platelet faces are oriented either parallel or perpendicular to the specimen flat surface, were prepared and the orientation of the particles was assessed by X-ray diffraction. Oscillatory rheological measurements in the linear viscoelastic regime were carried out. The in-plane and out-of-plane shear behavior was measured and the Halpin-Tsai structural parameter ζ calculated. For in-plane shear, ζ slightly decreased with increasing aspect ratio, whereas for out-of-plane shear, ζ strongly increased. Surface treatment of the mica particles had practically no influence on the results in the investigated loading range (volume fraction ≤7%).     

Effect of nanoplatelet aspect ratio on mechanical properties of epoxy nanocomposites

To study the effect of the aspect ratio of nanoplatelets on the mechanical properties of polymer nanocomposites, epoxy/α-zirconium phosphate nanocomposites with two distinctive aspect ratios at ca. 100 and 1000 have been prepared and characterized. Scanning electron microscopy and transmission electron microscopy were utilized to confirm the two different sizes and aspect ratios of nanoplatelets in epoxy. As expected, it is found that mechanical properties of the nanocomposite are affected by the aspect ratio of nanoplatelets in epoxy. That is, a higher aspect ratio renders a better improvement in modulus. It is also found that the interfacial characteristics between the nanoplatelets and polymer matrix are most critical in affecting the strength and ductility of the polymer. The operative fracture mechanisms depend strongly on the aspect ratio of the nanoplatelets incorporated. The crack deflection mechanism, which leads to a tortuous path crack growth, is only observed for the high aspect ratio system. The implication of the present findings for structural applications of polymer nanocomposites is discussed.     

The influence of carbon nanotube aspect ratio on the foam morphology of MWNT/PMMA nanocomposite foams

Polymer nanocomposite foams, products from the foaming of polymer nanocomposites, have received increasing attention in both the scientific and industrial communities. Nanocomposite foams filled with carbon nanofibers or carbon nanotubes with high electrical conductivity, enhanced mechanical properties, and low density are potential effective electromagnetic interference (EMI) shielding materials. The EMI shielding efficiency depends on the electrical conductivity and bubble density, which in turn, depend on the properties of the filler. In the current study, multi walled carbon nanotubes (MWNT) with controlled aspect ratio were used to alter the bubble density in MWNT/poly(methyl methacrylate) (PMMA) nanocomposites. It was found that the nanocomposite foams filled with shorter MWNT had higher bubble density under the same foaming conditions and MWNT concentration. Both the ends and sidewalls of carbon nanotubes can act as heterogeneous bubble nucleation sites, but the ends are more effective compared to the sidewalls. Shorter nanotubes provide more ends at constant MWNT concentration compared to long nanotubes. As a result, the difference in the foam morphology, particularly the bubble density, is due to the difference in the number of effective bubble nucleation sites.     

Structure and property study of nylon‐6/clay nanocomposite fiber

The crystal structures of nylon‐6 and nylon‐6/clay fibers were investigated on annealing and drawing. Annealing increased the γ‐crystalline form of both fibers, as indicated by the DSC curves, and its effect was dominant in nylon‐6/clay fiber. On drawing, the γ‐crystalline form was easily converted into the α form in nylon‐6, whereas it was still observed at a relatively high spin‐draw ratio in nylon‐6/clay fiber. However, although the α‐crystal form was dominant in nylon‐6, the γ‐crystal form was dominant in nylon‐6/clay with annealing and drawing, on the basis of the XRD data. The fast crystallization rate of nylon‐6/clay compared with pure nylon‐6 was confirmed, on the basis of the Avrami exponent. The initial modulus of nylon‐6/clay fiber was 30 % higher than the neat nylon‐6 fiber. The reinforcing effect of clay on the dynamic storage modulus was observed. Copyright © 2004 Society of Chemical Industry     

Crystallization behavior of nylon-6 confined among ultra-fine full-vulcanized rubber particles

The crystallization behavior of nylon-6 confined in a hybrid of nylon-6 and ultra-fine full-vulcanized powdered rubber was studied. It is found that carboxylic styrene-butadiene ultra-fine full-vulcanized powdered rubber (CSB-UFPR) could behave as a nucleating agent for nylon-6 crystallization, which can increase the crystallization temperature, the onset temperature of crystallization as well as the glass transition temperature of nylon-6 confined in the hybrid of nylon-6 and ultra-fine full-vulcanized powdered rubber. It is also found that nylon-6 molecules confined among CSB-UFPR particles favor the crystalline form of γ than that of α. The crystallization process of γ phase of nylon-6 in nylon-6/CSB-UFPR hybrid is a diffusion-controlled process, and thus it can be accelerated by raising the crystallization temperature or by extending oil into CSB-UFPR. It is expected that these results will benefit the research on crystallization behavior of other constrained geometry polymer, such as ultra-thin film and polymer/clay hybrid, and etc.     

Nanoindentation and morphological studies on injection-molded nylon-6 nanocomposites

The nanoindentation behavior and morphology of the injection-molded specimens of nylon-6 (PA6)/clay nanocomposites prepared by melt-compounding have been studied in present study. The elastic and plastic properties as well as creep behavior of PA6 and its nanocomposites are comparatively evaluated as the function of clay loading by using nanoindentation technique. The anisotropic characteristics in mechanical properties are studied by indenting the injection-molded specimens in two different directions (i.e. parallel and perpendicular to the injection direction). The uneven distribution of both the clay nanofiller and the crystallinity of the polymeric matrix induced by melt-processing leads to the variation of the mechanical property of the nanocomposites in certain directions and locations within the molded specimens. The microstructural and morphological changes of PA6 upon incorporating with clay nanofiller are evidenced by transmission electron microscopy and small-angle X-ray scattering, which are closely correlated with the anisotropy of the mechanical properties observed by nanoindentation.     

尼龙6/蒙脱土纳米复合材料的合成新方法

利用微波加热交换法分两步将浮选后的天然钠基蒙脱土转变为镍基蒙脱土,通过配位理论把单体引入镍基蒙脱土层间,制得尼龙6/蒙脱土纳米复合材料。为制备尼龙6/蒙脱土纳米复合材料提供了一种新方法。     

Effects of processing history and annealing on polymorphic structure of nylon-6/montmorillonite nanocomposites

The effects of processing history and annealing treatment on the thermal property and polymorphic structure of nylon-6/clay nanocomposites (NCNs) have been investigated. The nanocomposites, including intercalated and exfoliated ones, were prepared by extruding nylon-6 (N6) with sodium montmorillonite (Na-MMT) or organo-montmorillonite (OMMT), respectively. DSC analysis revealed multiple melting endotherms in either the extruded or the injection-molded N6 and NCNs samples. It has been observed that a small exothermic peak around 195 °C just before the lower melting peak in the skin regions. We demonstrated that this sub-T_m transition was directly related to the processing-induced shear stresses. WAXD analysis was further performed to characterize the polymorphic structure of injection-molded N6 and NCNs before and after annealing. Annealing at a temperature (80 °C) above the T_g of N6 resulted in increase of the absolute content of γ-form in the skin regions and of the relative content of γ-form in the core regions of NCNs. In particular, annealing only leaded to increase the fraction of γ-form in the exfoliated N6/OMMT nanocomposites, which might be related to a confining effect of MMT platelet on the polymer chains mobility.     

Phase transition in nylon 6/clay nanocomposites on annealing

The γ→α crystalline phase transition in nylon 6/clay nanocomposite prior to melting was investigated by X-ray diffraction. The phase transition in the nanocomposite took place at 160 °C, 40 °C higher than that of nylon 6 at 120 °C. The transition extent in the nanocomposite was lower than that in nylon 6. This could be caused by the strongly confined spaces between layers, and the favorable environment for the formation of the γ phase in the existence of clay. Besides, the less grown crystallites of the α phase transformed from the γ phase in the nanocomposite began to melt at much lower temperature than its normal melting temperature.     

Effects of aspect ratio of MWNT on the flammability properties of polymer nanocomposites

The effects of the aspect ratio of multi-walled carbon nanotubes (MWNTs) on the rheology and flammability of polystyrene/MWNT nanocomposites are studied using two MWNTs having average aspect ratios (length to outer diameter) of 49 and 150. Dynamic rheological experiments show that the particles with the larger aspect ratio impart much higher storage moduli and complex viscosities to the nanocomposites compared to equivalent mass loadings of particles with the smaller aspect ratio. Additionally, in flammability experiments, the larger aspect ratio particles lead to a greater reduction in mass loss rate, i.e., they are more effective at reducing flammability. These results demonstrate that the aspect ratio of MWNTs is a key parameter in controlling the rheology and flammability of polymer nanocomposites.     

Equilibrium swelling behavior and elastic properties of polymer–clay nanocomposite hydrogels

Nanocomposite hydrogels were prepared by free‐radical polymerization of the monomers acrylamide (AAm), N,N‐dimethylacrylamide (DMA), and N‐isopropylacrylamide (NIPA) in aqueous clay dispersions at 21°C. Laponite XLS was used as clay nanoparticles in the hydrogel preparation. The hydrogels based on DMA or NIPA monomers exhibit much larger moduli of elasticity compared with the hydrogels based on AAm monomer. Calculations using the theory of rubber elasticity reveal that, in DMA‐clay or NIPA‐clay nanocomposites, both the effective crosslink density of the hydrogels and the functionality of the clay particles rapidly increase with increasing amount of Laponite up to 10% (w/v). The results suggest that DMA‐clay and NIPA‐clay attractive interactions are stronger than AAm‐clay interactions due to the formation of multiple layers on the nanoparticles through hydrophobic associations. It was also shown that, although the nanocomposite hydrogels do not dissolve in good solvents such as water, they dissolve in dilute aqueous solutions of acetone or poly(ethylene oxide) of molecular weight 10,000 g/mol, demonstrating the physical nature of the crosslink points. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Modeling of polymer/clay nanocomposite formation

A statistical thermodynamic modeling of the formation of polymer/clay intercalation and nanocomposites was developed. The key factor in determining intercalation was an exothermic heat of mixing between polymer chains and the organically modified silicate surface. This was found to agree with previous experimental results in the literature including halogenated polymers and acrylonitrile copolymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1657–1663, 2006     

Studies on nylon 6/clay nanocomposites by melt‐intercalation process

The preparation of nylon 6/clay nanocomposites by a melt‐intercalation process is proposed. X‐ray diffraction and DSC results show that the crystal structure and crystallization behaviors of the nanocomposites are different from those of nylon 6. Mechanical and thermal testing shows that the properties of the nanocomposites are superior to nylon 6 in terms of the heat‐distortion temperature, strength, and modulus without sacrificing their impact strength. This is due to the nanoscale effects and the strong interaction between the nylon 6 matrix and the clay interface, as revealed by X‐ray diffraction, transmission electron microscopy, and Molau testing. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1133–1138, 1999     

Investigation of polymer and nanoclay orientation distribution in nylon 6/montmorillonite nanocomposite

A method to determine the orientation distribution function of montmorillonite clay in nylon 6 nanocomposite films by a combination of infrared (FTIR) trichroic analysis and transmission electron microscopy (TEM) image analysis is described. The structural absorbance of the nanoclay Si-O vibrations was obtained by the sample tilting method described by Schmidt [Schmidt PG. J Polym Sci: Part A 1963;1:1271-1292]. A nonlinear least squares regression was performed to extract the absorbance of individual peaks. The montmorillonite clay orientation in spun cast nylon 6 films can be described by a Gaussian function having a standard deviation of 15° i.e. 95% of the clay platelets are tilted at an angle of within ±30° of the plane of the film. The transition dipole moment angles of the 1018 and 1046 cm⁻¹ clay vibrations are determined to be 18 and 16° relative to the clay surface, respectively. The orientation of nylon 6 in the nanocomposite was also investigated based on the NH stretching mode. The NH bonds are found to be less preferentially oriented along the plane of the film surface compared to pure nylon 6 film.     

Relation between ductility and segmental mobility of nylon-6

High-resolution solid-state ¹⁵N and ¹³C NMR and dynamic mechanical measurements were carried out for solution grown crystals of the α- and γ-forms of nylon-6 to understand the relation between segmental mobility including interchain interactions and ductility of polyamides. The ductility, in the temperature range of 100-180 °C, was lower for the α-crystals than for γ-crystals. ¹⁵N chemical shift revealed that the hydrogen bonding was stronger for the γ-crystals than for α-crystals. In addition, lower mobility of NH group in the γ-crystals than in α-crystals was shown by results. The results suggest that the ductility of nylon-6 could not be simply related to the strength of hydrogen bonding. Highly crystalline films of aggregates of solution grown α-crystals and γ-crystals showed no crystalline relaxation in the temperature dependence of dynamic mechanical loss factor, suggesting an existence of strong intermolecular interactions in the crystalline regions although data indicated that the mobility of methylene units was higher in the γ-crystals than in α-crystals. Information on the large-scale chain dynamics in the crystalline regions might be necessary to understand the low ductility of polyamides.     

Unique clay orientation in the injection-molded bar of isotactic polypropylene/clay nanocomposite

In this article, the injection-molded bars of isotactic polypropylene/organoclay nanocomposite with different clay contents have been obtained via dynamic packing injection molding (DPIM). The oriented microstructure including layered nanoparticles and PP lamellae has been inspected through 2D-WAXS analyses along the sample thickness of the molded bars. Depending on the clay content and sample thickness, various oriented clay structures with nanoparticles uniplanar-axially oriented parallel to the surface of molded bar, or partially tumbled around the flow axis of the molded bar, or even a random orientation, could be observed. The observed orientation behavior of nanoparticles could be temporarily elucidated as the results of the sensitive response of layered nanoparticles to shear deformation and the structural recovery of clay network assisted by the electrostatic attraction existing between adjacent nanoplatelets.     

Studies on electrospun nylon-6/chitosan complex nanofiber interactions

Composite membranes of nylon-6/chitosan nanofibers with different weight ratio of nylon-6 to chitosan were fabricated successfully using electrospinning. Morphologies of the nanofibers were investigated by scanning electron microscopy (SEM) and the intermolecular interactions of the nylon-6/chitosan complex were evaluated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) as well as mechanical testing. We found that morphology and diameter of the nanofibers were influenced by the concentration of the solution and weight ratio of the blending component materials. Furthermore FT-IR analyses on interactions between components demonstrated an IR band frequency shift that appeared to be dependent on the amount of chitosan in the complex. Observations from XRD and DSC suggested that a new fraction of γ phase crystals appeared and increased with the increasing content of chitosan in blends, this indicated that intermolecular interactions occurred between nylon-6 and chitosan. Results from performance data in mechanical showed that intermolecular interactions varied with varying chitosan content in the fibers. It was concluded that a new composite product was created and the stability of this system was attributed to strong new interactions such as hydrogen bond formation between the nylon-6 polymers and chitosan structures.     

Morphology and crystallization behavior of nylon 6‐clay/neat nylon 6 bicomponent nanocomposite fibers

Nylon 6‐clay hybrid/neat nylon 6, sheath/core bicomponent nanocomposite fibers containing 4 wt % of clay in sheath section, were melt spun at different take‐up speeds. Their molecular orientation and crystalline structure were compared to those of neat nylon 6 fibers. Moreover, the morphology of the bicomponent fibers and dispersion of clay within the fibers were analyzed using scanning electron microscopy and transmission electron microscopy (TEM), respectively. Birefringence measurements showed that the orientation development in sheath part was reasonably high while core part showed negligibly low birefringence. Results of differential scanning calorimetry showed that crystallinity of bicomponent fibers was lower than that of neat nylon 6 fibers. The peaks of γ‐crystalline form were observed in the wide‐angle X‐ray diffraction of bicomponent and neat nylon 6 fibers in the whole take‐up speed, while α‐crystalline form started to appear at high speeds in bicomponent fibers. TEM micrographs revealed that the clay platelets were individually and evenly dispersed in the nylon 6 matrix. The neat nylon 6 fibers had a smooth surface while striped pattern was observed on the surface of bicomponent fibers containing clay. This was speculated to be due to thermal shrinkage of the core part after solidification of the sheath part in the spin‐line. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39996.     

SBR粘土纳米复合材料的气密性

对乳液法制备的SBR粘土纳米复合材料的气密性进行了研究,结果表明：SBR粘土纳米复合材料的气密性优于传统填料填充的硫化胶,且随温度的变化较小;填料的用量、形状以及与橡胶的结合性是影响气密性的主要因素;填充20份粘土的纳米复合材料气密性优于NR／SBR内胎,比IIR内胎差。     

Effect of lactic acid on polymer crystallization chain conformation and fiber morphology in an electrospun nylon-6 mat

The role of lactic acid (LA) on the polymer crystallization chain conformation and the surface modification of the electrospun nylon-6 fibers were examined. The effect of different amounts of LA on the polymer crystallization chain conformation of nylon-6 mat was evaluated using XRD, FT-IR and Raman spectroscopy whereas the surface modification of the electrospun mats was examined by FE-SEM, contact angle and mechanical properties measurement. It was found that the transition of meta-stable γ-form into the thermodynamically stable α-form was achieved by increasing the amounts of LA in the blend mixture. The adhesive property of LA was found to be responsible for the transformation from non-bonded to the point-bonded structure of nanofibers in the electrospun nylon-6 mat. The resultant LA/nylon-6 hybrid mat with improved hydrophilicity and mechanical properties may be a potential candidate for tissue scaffold.