Multiple melting and crystallization of nylon‐66/montmorillonite nanocomposites

Nylon‐66 nanocomposites were prepared by melt‐compounding nylon‐66 with organically modified montmorillonite (MMT). The organic MMT layers were exfoliated in a nylon‐66 matrix as confirmed by wide‐angle X‐ray diffraction (WAXD) and transmission electron microscopy. The presence of MMT layers increased the crystallization temperature of nylon‐66 because of the heterogeneous nucleation of MMT. Multiple melting behavior was observed in the nylon‐66/MMT nanocomposites, and the MMT layers induced the formation of form II spherulites of nylon‐66. The crystallite sizes L₁₀₀ and L₀₁₀ of nylon‐66, determined by WAXD, decreased with an increasing MMT content. High‐temperature WAXD was performed to determine the Brill transition in the nylon‐66/MMT nanocomposites. Polarized optical microscopy demonstrated that the dimension of nylon‐66 spherulites decreased because of the effect of the MMT layers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2861–2869, 2003     

Polymorphism in nylon‐11/montmorillonite nanocomposite

The polymorphism behavior in nylon‐11/montmorillonite (MMT) nanocomposite was investigated by wide‐angle X‐ray diffraction (WAXD) and variable‐temperature infrared spectroscopy. The results of WAXD and IR confirmed the presence of the γ‐crystalline form of nylon‐11, which is induced and stabilized by MMT. However, the hydrogen bond in the nanocomposite and its temperature dependence also exhibited some differences from neat nylon‐11. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 253–259, 2004     

Rheological properties of ferrite nanocomposites based on nylon‐66

Effects of ferrite nanoparticles (0.1–20 wt %) on the rheological and other physical properties of nylon‐66 were investigated. The presence of ferrite nanoparticles less than 1 wt % increased the crystallization temperature (T_c) by 4.2 °C with ferrite content, but further addition decreased T_c. The onset temperature of degradation was increased by 7.3 °C at only 0.1 wt % loading of ferrite, after which the thermal stability of nylon‐66 was decreased with ferrite content. The incorporation of ferrite nanoparticles more than 5 wt % increased the dynamic viscosity (η′) with the loading level. Further, it produced notably shear thickening behavior in the low frequency, after which high degree of shear thinning was followed with ferrite content. In the Cole–Cole plot, the nanocomposites with ferrite lower than 5 wt % presented a single master curve, while further addition gave rise to a deviation from the curve. The relaxation time (λ) was increased with ferrite content and the difference of λ between nylon‐66 and its nanocomposite was greater at lower frequency. The tensile strength was a little increased up to 1 wt % loading, after which it was decreased with increasing the loading level. In addition, the introduction of the nanoparticles increased tensile modulus and decreased the ductility with ferrite content. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 371–377, 2006     

Phase transition in polyamide‐66/montmorillonite nanocomposites on annealing

The crystalline‐phase transition in polyamide‐66/montmorillonite nanocomposites before melting was investigated by in situ X‐ray diffraction and is reported for the first time in this work. The phase‐transition temperature in the nanocomposites was 170 °C, 20 °C lower than that in polyamide‐66. The lower phase‐transition temperature of the nanocomposites could be attributed to the γ‐phase‐favorable environment caused by silicate layers. Meanwhile, the addition of silicate layers changed the crystal structure of the polyamide‐66 matrix and influenced the phase‐transition behavior. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 63–67, 2003     

Water‐assisted melt compounding of nylon‐6/pristine montmorillonite nanocomposites

An exploratory pioneering study on the fabrication of nylon‐6/montmorillonite (MMT) nanocomposites with the aid of water as an intercalating/exfoliating agent via melt compounding in a twin‐screw extruder was conducted. Commercial nylon‐6 pellets and pristine MMT powder were directly fed into the hopper of the extruder. Water was then injected into the extruder downstream. After interactions with the nylon‐6 melt/pristine MMT system, water was removed from the extruder further downstream via a venting gate. As such, no third‐component residual was left within the extrudates. Transmission electron microscopy micrographs showed that pristine MMT was uniformly dispersed in the nylon‐6 matrix. The contact time between water and the nylon‐6/pristine MMT system inside the extruder was so short that nylon‐6 was subjected to very little hydrolysis, if any. The resultant nanocomposites showed higher stiffness, superior tensile strength, and improved thermal stability in comparison with their counterparts obtained without water assistance and the nylon‐6/organic MMT nanocomposites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1100–1112, 2005     

Unusual Crystallization Behavior in Nylon‐6 and Nylon‐6/Montmorillonite Nanocomposite Films

Summary: The crystallization behavior of nylon‐6 and nylon‐6/montmorillonite nanocomposite films with different heat histories was investigated by wide‐angle X‐ray diffraction (WAXD). For nylon‐6 films isothermally crystallized above 170 °C or annealed at 200 °C and then quenched in ice water, a crystalline peak appeared at 2θ = 28.5°. This crystalline peak was strong in intensity for the former and weak for the latter. However, for nylon‐6 films cooled in air after isothermal crystallization or annealing, no crystalline peak at 2θ = 28.5° was observed in the WAXD patterns. For nylon‐6/montmorillonite nanocomposite films annealed above 140 °C, a crystalline double peak was observed between the α1 and α2 peaks. The possible origins of the peak at 2θ = 28.5° and the crystalline double peak are discussed.

WAXD patterns of isothermally crystallized nylon‐6/montmorillonite nanocomposite films.     

Preparation and properties of poly(vinyl alcohol)–vermiculite nanocomposites

A vermiculite (VMT) dispersion in water was blended with aqueous poly(vinyl alcohol) (PVA). The properties of the PVA–VMT nanocomposites greatly depended on the preparation procedure because of the chemical reactions and physical interactions involved. The samples were prepared in two steps to investigate the properties of the PVA–VMT nanocomposites. The VMT was first pretreated and delaminated with hydrochloric acid. The delaminated VMT was then added to the PVA solution with various mixing times. The structure and properties of the films were investigated. From X‐ray diffraction and transmission electron microscopy, the VMT layers were found to be well dispersed individually in the PVA–VMT blends. The effect of the VMT content on the thermal behavior of the PVA–VMT blends was also studied with differential scanning calorimetry. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 749–755, 2003     

Polymer crystalline structure and morphology changes in nylon‐6/ZnO nanocomposites

The influence of ZnO nanoparticles on the crystalline structures of nylon‐6 under different crystallization conditions (annealing at different temperatures from the amorphous solid, isothermal crystallization from the melt at different temperatures, and crystallization from the solution) has been examined with differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared. ZnO nanoparticles can induce the γ‐crystalline form in nylon‐6 when it is cooled from the melted state and annealed from the amorphous solid. This effect of ZnO nanoparticles increases with decreasing particle size and changes under different crystallization conditions. The effects of ZnO nanoparticles on the crystallization kinetics of nylon‐6 have also been studied with DSC. The results show that ZnO nanoparticles have two competing effects on the crystallization of nylon‐6: inducing the nucleation but retarding the mobility of polymer chains. Finally, the melting behavior of the composites has been investigated with DSC, and the multiple melting peaks of composites containing ZnO nanoparticles and pure nylon‐6 are ascribed to the reorganization of imperfect crystals. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1033–1050, 2003     

Simulation of solid‐state polycondensation of nylon‐66

A new model of solid‐state polymerization of nylon‐6,6 has been developed. The polymer crystalline fraction is assumed to consist of only repeat units, leaving end‐groups and condensate in the amorphous fraction. Many effects neglected by previous models are considered, such as variable crystallinity, initial moisture and starting molecular weight. This model is compared to experimental data with good agreements. Differential scanning calorimetry graphs show that the crystalline structure phase tends to be increasingly perfect during heat treatment, indicative of the premelting temperature drawing near the melting point up to 14 °C after solid‐state polycondensation with little change of melting point. Copyright © 2000 John Wiley & Sons, Ltd.     

Synthesis and characterization of polyurethane‐urea clay nanocomposites using montmorillonite modified by oxyethylene–oxypropylene copolymer

Clay organifier with propylene oxide‐capped polyethylene glycol (PEG) with amine end group (jeffamines ED_600–2003) was synthesized through an ion exchange process between sodium cations in montmorillonite (MMT) and ? NH groups in ED_600–2003. The d‐spacing of organoclay was found to be 1.697–1.734 nm compared to 0.96 nm of pristine MMT. Transmission electron microscopy (TEM) was used to determine the molecular dispersion of the clay within ED₆₀₀. Polyurethane‐urea/montmorillonite (PUU‐MMT) nanocomposites were prepared via in situ polymerization from polyethylene glycol (PEG 400) or 1,4 butane diol (1,4 BD), toluene diisocyanate (TDI), jeffamines ED_600–2003, and 1–12 wt% of organoclay. Intercalation of PUU into modified clays was confirmed by X‐ray diffraction (XRD), scanning electron microscopy, and TEM. The barrier properties were significantly reduced; however, the thermal stability was increased in the nanocomposites as compared to the pristine polymer. Nanocomposites exhibited optical clarity and solvent resistance. The mechanical properties and the glass transition temperature of PUU were improved with the addition of organoclay. The incorporation of silicate layers gave rise to a considerable increase in the storage modulus (stiffness), demonstrating the reinforcing effect of clay on the PUU matrix. Copyright © 2009 John Wiley & Sons, Ltd.     

Structures of X 34‐nylons in chain‐folded lamellae and gel‐spun fibers

Structural studies and morphological features of a new family of linear, aliphatic even–even, X 34‐nylons, with X = 2, 4, 6, 8, 10, and 12, are investigated with X‐ray diffraction and electron microscopy. Solution‐grown crystals were obtained by isothermal crystallization from N,N‐dimethylformamide solutions. The thickness of lamellar‐like crystals was orders of magnitude less than the chain lengths of the polymer samples used, implying that the chains fold to form chain‐folded lamellae. The results bear a close resemblance, with the noticeable exception of 2 34‐nylon, to those reported for nylon 6 6 and other even–even nylon chain‐folded lamellar crystals. The basic structure of the straight‐stem lamellar core is similar to that of the classic nylon 6 6 triclinic α structure, and the chains tilt ≈42° relative to the lamellar normal. In the case of 2 34‐nylon, the structure resembles the 2 Y nylon series, and the chain tilt angle reduces to 36.6°. These combined results suggest that, even with a relatively low frequency of amide units along the backbone of these molecules, hydrogen bonding is still the dominant element in controlling the behavior, structure, and properties of these polymers. In addition, gels were prepared in concentrated sulfuric acid, and gel‐spun fibers were studied using X‐ray diffraction. The data are interpreted in terms of a modified nylon triclinic α structure that bears a resemblance to the structure of even–even nylons at elevated temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2685–2692, 2002     

An acrylic acid modified polypropylene as a compatibilizing agent for the intercalation/exfoliation of an organically modified montmorillonite in polypropylene

This work dealt with the effect of using an acrylic acid modified polypropylene (PP‐g‐AA) as a compatibilizing agent for the intercalation/exfoliation of an organically modified montmorillonite (o‐MMT) in a polypropylene matrix (PP). Two PP‐g‐AA containing the same AA content (6 wt %) and having different molar masses were used. The o‐MMT content was 0, 1, or 5 wt % of total mass and the PP‐g‐AA/o‐MMT mass ratio was 0/1, 1/1, 2/1, or 5/1. Results of wide angle X‐ray scattering (WAXS) and transmission electronic microscopy (TEM) showed that without the PP‐g‐AA, the o‐MMT was dispersed in the PP/o‐MMT in a micrometer scale, similar to a conventional microcomposite. With the PP‐g‐AA, the o‐MMT was much better dispersed and its interlayers were intercalated and partly exfoliated by the polymer chains. Compared with the neat PP, some PP/PP‐g‐AA/o‐MMT systems exhibited higher G′ values and a yield stress at low frequencies, indicating that the PP‐g‐AA promoted the intercalation/exfoliation of the o‐MMT. The compatibilizing efficiency of those two PP‐g‐AA was very similar. Generally speaking, the higher the PP‐g‐AA/o‐MMT mass ratio, the better the state of dispersion and the degree of intercalation/exfoliation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1811–1819, 2008     

Synthesis,rheology, and morphology of nylon‐11/layered silicate nanocomposite

Exfoliated nylon‐11/layered silicate nanocomposites were prepared via in situ polymerization by dispersing organoclay in 11‐aminoundecanoic acid monomer. The original clay was modified by a novel method with 11‐aminoundecanoic acid. In situ Fourier transform infrared spectroscopy results show that stronger hydrogen bonds exist between nylon‐11 and organoclay than that of between nylon‐11 and original clay. The linear dynamic viscoelasticity of organoclay nanocomposites was investigated. Before taking rheological measurements, the exfoliated and intercalating structures and the thermal properties were characterized using X‐ray diffraction, transmission electron microscopy, differential scanning calorimetry, and thermogravimetric analysis. The results show that the clay was uniformly distributed in nylon‐11 matrix during in situ polymerization of clay with 4 wt % or less. The presence of clay in nylon‐11 matrix increased the crystallization temperature and the thermal stability of nanocomposites prepared. Rheological properties such as storage modulus, loss modulus, and relative viscosity have close relationship with the dispersion favorably compatible with the organically modified clay. Comparing with neat nylon‐11, the nanocomposites show much higher dynamic modulus and stronger shear thinning behavior. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2161–2172, 2006     

Effect of silver nanoparticles on the dynamic crystallization behavior of nylon‐6

The effect of introducing silver nanoparticles on the rheological properties and dynamic crystallization behavior of nylon‐6 was investigated. The nanocomposites showed slightly higher viscosity than pure nylon‐6 in the low‐frequency range even at an extremely low loading level of the silver particles (0.5–1.0 wt %). The nanoparticles had a more noticeable effect on the storage modulus than on the loss modulus of a nylon‐6 melt and reduced its loss tangent. They increased the crystallization temperature of nylon‐6 by about 14 °C and produced a sharper crystalline peak. The silver nanoparticles promoted the crystallization of nylon‐6, and their effect on the dynamic crystallization of nylon‐6 at 200 °C was more notable at a lower shear rate and at 190 °C at a higher frequency. Nylon‐6 produced large spherulitic crystals, but the nanocomposites showed a grainy structure. In addition, the silver nanoparticles reduced the fraction of the α‐form crystal but increased that of the γ‐form crystal. The nanocomposites crystallized at 190 °C showed a lower melting temperature than nylon‐6 by about 3 °C, whereas the nanocomposites crystallized at 200 °C showed almost the same melting temperature. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 790–799, 2004     

Polymorphism of nylon‐6 in multiwalled carbon nanotubes/nylon‐6 composites

The effects of pristine and amino‐functionalized multiwalled carbon nanotubes (MWNTs) on the crystallization behaviors of nylon‐6 were investigated by differential scanning calorimetry and X‐ray diffraction. The results indicate the presence of polymorphism in nylon‐6 and its composites, which is dependent on the MWNTs concentration and the cooling rate. More MWNTs and slow cooling from the melt favors the formation of α crystalline form. With the increase in cooling rates, the crystallinity of neat nylon‐6 decreases, and that of the composites decreases initially but increases afterward. Moreover, the degree of crystallinity of the composites is higher than neat nylon‐6 under high cooling rates, counter to what is observed under low cooling rates. The heterogeneous nucleation induced by MWNTs and the restricted mobility of polymer chains are considered as the main factors. Furthermore, addition of MWNTs increases the crystallization rate of α crystalline form but amino‐functionalization of MWNTs weakens this effect. The influence of thermal treatment on the crystalline structure of MWNTs/nylon‐6 composites is also discussed. A γ–α phase transition takes place at lower temperature for MWNTs/nylon‐6 composites than for nylon‐6. The annealing peaks of the composites annealed at 160 °C are higher than that of neat nylon‐6, and the highest annealing peak is obtained for amino‐functionalized MWNTs/nylon‐6 composites. This phenomenon is closely related to the different nucleation and recrystallization behaviors produced by various MWNTs in confined space. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1499–1512, 2006     

Large‐scale extrusion processing and characterization of hybrid nylon‐6/SiO2 nanocomposites

Solution impregnations, pulltrusion and film stacking are widely used methods to prepare thermoplastic composite materials. Extruders are used to melt the polymer and to incorporate fibers into the polymer in order to modify physical properties. In this article, the compounding of colloidal silica nanoparticles filled polyamide‐6 (PA‐6) is achieved using a twin‐screw extruder, which has a significant market share due to its low cost and easy maintenance. The experiments were performed at 250 rpm and the bulk throughput was 6 kg h^?1 with a pump pressure of 30 bars. The composites were characterized with nuclear magnetic resonance (NMR), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). As determined by WAXD, the PA‐6 showed higher amounts of γ‐phase when compared to other synthesis methods such as in situ polymerization. TEM pictures showed that the silica particles aggregated nevertheless, upon addition of 14% (w/w) silica the E‐modulus increased from 2.7 to 3.9 GPa indicating that an effective mechanical coupling with the polymer was achieved. The behavior, illustrated with dynamic mechanical analysis (DMA) curves, indicated that in general when a filled system is compared to unfilled material, the values of the moduli (E′ and E″) increased and tan δ decreased. Determination of molecular mass distribution of the samples by means of size exclusion chromatography (SEC) coupled to a refractive index (RI), viscosity (DV) and light scattering (LS) detector revealed that the addition of silica did not decrease the average molecular weight of the polymer matrix, which is of importance for composite applications. Copyright © 2004 John Wiley & Sons, Ltd.     

Relaxation peak broadening and polymer chain dynamics in aramid‐fiber‐reinforced nylon‐66 microcomposites

The relationship between the parameter of symmetric broadening of the glass‐transition relaxation process and the structure of aramid‐fiber‐reinforced nylon‐66 microcomposites is investigated in this article. The approach is based on a previously derived model that sets a quantitative interrelation between the Cole–Cole parameter α, the relaxation time, and the fractal dimension of a mobile polymer segment. The microcomposite, the dielectric response of which reflects the transcrystallinity effects, indeed exhibits significantly different values, such as higher Kirkwood correlation factor and α exponent values, in comparison with the control materials, and this indicates its different crystalline morphology and perhaps lower order in the amorphous phase. However, at this stage, it is still difficult to establish a quantitative relationship with the polymer chain dynamics. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 217–223, 2003     

Molecular composites prepared by in situ direct synthesis of wholly aromatic rigid‐rod polyamides via the phosphorylation reaction in a dissolved nylon‐6 matrix

Wholly aromatic rigid‐rod polyamides such as poly(p‐phenyleneterephthalamide) (PPD‐T) were synthesized in situ in a solution of nylon‐6 via the phosphorylation polycondensation method to form nanocomposites or so‐called “molecular composites.” The incorporation of PPD‐T into a nylon‐6 matrix was achieved by this approach in a more compatibilized form than that obtained by the conventional coagulation method that entails precipitation of a blend of PPD‐T and nylon‐6 in a solvent, for example, concentrated sulfuric acid. Gelation occurred during the synthesis, presumably because of the formation of interpenetrating networks accompanied by some block‐copolymer formation. The transparency and tensile properties of the resultant composite films from the rigid‐rod aromatic polyamide/nylon‐6 combination were improved over those of nylon‐6 film alone. Rainbow‐colored intense birefringence was observed for the composite films under crossed polarizers. These properties are discussed in context with the in situ synthesized rigid‐rod polyamides uniformly incorporated in nylon‐6. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1014–1026, 2003