Effect of interfacial interaction on the structure and rheological properties of polyamide-6/clay nanocomposites

A series of polyamide-6 (PA6)/layered silicate (clay) nanocomposites were prepared via direct melt compounding using a conventional single screw extruder, and then the effect of interfacial interaction on the characteristic internal structure and rheological properties of PA6/clay nanocomposites was investigated. XRD diffractograms indicated a large extent of exfoliation of the layered silicate entering into a strong interaction with PA6. The formation of such morphology was further supported by TEM images. In addition, various rheological properties were interpreted in conjunction with morphological characteristics depending on interfacial interaction between PA6 and the layered silicate.     

Mechanical,Thermal, and Surface Properties of Ultrahigh Molecular Weight Polyethylene/Polypropylene Blends

Various compositions of ultrahigh molecular weight polyethylene/polypropylene (UHMWPE/PP) blends were prepared in decalin, with the rheological, mechanical, thermal, and surface properties of the blends being determined using the solution cast film. Viscosity and mechanical properties of the blends decreased below the additivity value with increasing PP content implying that PP molecules disturb the entanglement of UHMWPE. Contact angle of the blend films with a water drop increased with increasing content of PP. The atomic force microscope (AFM) images showed that the surface of cast UHMWPE was very smooth whereas that of cast PP was very uneven. For blends, the surface became rough and uneven with increasing content of PP. The melting temperature of PP (T _mP) decreased in the blends with increasing UHMWPE content while that of UHMWPE (T _mU) remained almost constant in blends.     

Structure and Mechanical Properties of 50/50 NR/SBR Blend/Pristine Clay Nanocomposites

A blend/clay nanocomposites of 50/50 (wt%) NR/SBR was prepared via mixing the latex of a 50/50 NR/SBR blend with an aqueous clay dispersion and co‐coagulating the mixture. The structure of the nanocomposite was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Nanocomposites containing less than 10 phr clay showed a fully exfoliated structure. After increasing the clay content to 10 phr, both nonexfoliated (stacked layers) and exfoliated structures were observed in the nanocomposites. The results of mechanical tests showed that the nanocomposites presented better mechanical properties than clay‐free NR/SBR blend vulcanizate. Furthermore, tensile strength, tensile strain at break, and hardness (shore A) increased with increasing clay content, up to 6 phr, and then remained almost constant.     

Friction and Wear Behavior of Polyamide 66/Poly(vinylidene fluoride) Blends

The tribological performance of PA66 and PVDF blends was investigated by a block‐on ring sliding friction and wear tester. The appropriate amount of PVDF can decrease the friction coefficient and improve the wear resistance of PA66. Moreover, the appropriate amount of PA66 can improve the wear resistance of PVDF. SEM analysis shows that PVDF is noncompatible with PA66, and the blend presents a two‐phase structure. A smooth worn surface is a main reason for improving the frictional and wear properties of the PA66/PVDF blend. Besides, slight debris is an important factor in improving the wear resistance of the PA66/PVDF blend. FT‐IR analysis shows that the oxidation and degradation behavior of PVDF is effectively controlled in the PA66/PVDF blends. Therefore, the blend of PA66 and PVDF is a potential polymer material for tribological applications.     

Synthesis of a Novel Flame Retardant and Its Synergistic Effect With a Phosphapheanthrene Flame Retardant in Polypropylene/Polyethylene Vinyl Acetate Blends

A novel flame retardant (NSiB) containing nitrogen, silicon and boron was synthesized through reacting of N-(β-aminoethyl)-γ-aminopropyl trimethoxy-silane (KH-792) and boric acid. The structure of NSiB was characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy with energy dispersive spectrometry (SEM-EDS). The effects of NSiB on the flame retardancy and thermal behaviors of polypropylene (PP)/polyethylene vinyl acetate (EVA) blends were investigated by limiting oxygen index value (LOI), vertical burning tests (UL-94) and thermal gravimetric analysis tests (TGA). The results showed that the flame retardancy and thermal stability of PP/EVA blends were improved with the addition of NSiB. When 7.5 wt% DOPO (phosphaphenanthrene) and 0.5 wt% NSiB were incorporated, the LOI value of the PP/EVA blends was 26.9%, and the class V-0 of UL-94 test was passed, as compared to the LOI value of 22.4% and class V-2 of UL-94 test for 8.0 wt% DOPO only and 16.7% and fail, respectively, for the PP/EVA blends alone. The char structure observed by SEM indicated that the surface of the char for the PP/EVA/7.5 wt% DOPO/0.5 wt% NSiB blends had a denser and continuous char structure when compared with that of the PP/EVA blends and PP/EVA/8.0 wt% DOPO blends. These results indicated that there was a good synergistic effect for NSiB and DOPO.     

A Kinetic Study on the Thermal Degradation of Polypropylene/Attapulgite Nanocomposites

In this work, a polypropylene (PP)/attapulgite nanocomposite was prepared via melt blending using a novel organically modified attapulgite (OATP). The thermal stability of PP/clay nanocomposites compared to pure PP was examined in nitrogen using a kinetic analysis. The kinetic parameters, including reaction order and activation energy (A and E _a) of the degradation process were determined by applying the Flynn‐Wall‐Ozawa method using derivative thermogravimetric (DTG) curves. At the same time, the effect of organic attapulgite on thermal decomposition of polypropylene matrix was analyzed. As a result, PP/OATP nanocomposites have slightly higher degradation temperature than that of the pure PP. The values of the reaction order of PP and PP/OATP nanocomposites are close to 1 in the nonisothermal degradation process. The activation energies of PP/OATP nanocomposites also increase slightly compared to the pure PP, thus it is suggested that the org‐attapulgite has little effect on the thermal stability of the pure PP.     

Effect of Nanoclay on the Morphology and Properties of Nylon 6 and Poly(Methyl Methacrylate) (PMMA) Blends

The effect of organomodified nanoclay on the morphology and properties of a (70/30 w/w) nylon 6/poly(methyl methacrylate) (PMMA) blend prepared by a melt processing method was investigated. The number average domain diameter (D_n ) of the dispersed PMMA phase was found to decrease with the addition of a small amount [0.5 per hundred resin (phr)] of clay in the blend. A much finer dispersion of the minor phase in the presence of a higher amount (5 phr) of clay indicated better mixing efficiency and improved morphology in the blend. X-ray diffraction indicated the exfoliation of the clays in the nylon 6 matrix, whereas PMMA chains only intercalated into the clay layers. However, the same effect of the clay was not observed in a (30/70 w/w) nylon 6/PMMA blend when nylon 6 became the dispersed domains. In the (30/70 w/w) nylon 6/PMMA blend, the addition of organomodified nanoclay (up to 2 phr) increased the D_n of the nylon 6 domains by preferential location of the clays inside the nylon 6 domains. Addition of styrene-maleic anhydride (SMA) copolymer effectively reduced the D_n of disperse phases in both compositions of the nylon 6/PMMA blends. Thus, in nylon 6/PMMA blends, clay platelets could prevent the coalescence of dispersed domains during melt mixing as long as it was dispersed in the matrix phase of the blend. Mechanical properties and thermal stability of the blends were also improved in the presence of clay.     

Surface functionalization, morphology and thermal properties of polyamide6/O-MMT composite nanofibers by Fe2O3 sputter coating

In the present work, the pure polyamide6 (PA6) nanofiber and PA6/organically modified montmorillonite (O-MMT) composite nanofiber were firstly prepared by a facile compounding process with electrospinning, and then coated by nanosize Fe₂O₃ using magnetron sputter technique. The effects of Fe₂O₃ sputter coating on structures, surface morphology and thermal stability were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), atomic force microscope (AFM) and thermogravimetric analyses (TGA), respectively. The SEM images showed that the diameters of composite nanofiber were decreased with the loadings of O-MMT and the nanosize Fe₂O₃ is well coated on the surface of the homogeneous and cylindrical nanofibers. The XPS spectra reflected the chemical features of the deposited nanostructures. The EDX confirmed the presence of the O-MMT and Fe₂O₃ in the fibers. The AFM observation revealed that there was a remarkable difference in the surface morphology of composite nanofiber before and after sputter coating. The TGA analysis indicated the barrier effects of silicate clay layers and catalysis effects of Fe₂O₃ improved thermal stability properties of the composite nanofiber.     

Long-Term Hydrothermal Aging Behavior and Aging Mechanism of Glass Fibre Reinforced Polyamide 6 Composites

Long-term hydrothermal aging of polyamide 6 (PA6)/glass fibre (GF) composites was conducted and the effects of the GF on variations of structure and properties of the composites with aging time were investigated. It was found that the first stage of aging was a Fickian process and corresponded to the physical absorption of water until equilibrium, resulting in a slight change of reduced viscosity and chemical structure of the PA6. The water diffusing process was slowed down slightly by addition of the GF. The second stage of aging was the initiation process of hydrolytic degradation of PA6, resulting in a rapid decrease of reduced viscosity and an increase of end group content. In the final stage of aging, the relative weight gain (W_r) dropped, the reduced viscosity decreased and the end groups increased slowly. The degradation rate and carbonyl index of PA6 increased with increasing GF content, and the increasing rate of end groups concentration of the composites was higher than that of pure PA6 during the aging process, indicating addition of GF accelerated the hydrolysis degradation and oxidative aging of PA6. In mechanical property tests, compared with unaged samples of the composites which underwent matrix rupture around the matrix-fiber interfacial layer, for aged samples several smooth fibres without coatings were pulled out and the interfacial debonding was the main failure mode, causing severe deterioration in mechanical properties. The hydrolytic degradation activation energy (E_a) was calculated through a method based on the Arrhenius model by considering both temperature and humidity as environment factors; with increasing GF content, E_a decreased, indicating that the addition of GF made PA6 easier to degrade.     

Adhesion in polyamide/compatibilizer/polypropylene systems

The effect of compatibilization on the adhesion, fracture toughness, morphology, and mechanical properties of isotactic polypropylene (PP)/polyamide 6 (PA) blends was investigated. Maleic anhydride (MAH) functionalized poly-(ethylene-co-vinyl acetate) (EVA-g-MAH) and nonreactive EVA copolymer were used as compatibilizers in binary blends. An attempt of in situ compatibilization via addition of pure maleic anhydride to PA/EVA/PP melt was also made. The blends containing maleated EVA copolymer showed more regular and finer dispersion of phases, better adhesion at the interface, and improved mechanical properties.     

Composite coatings of polyamide/graphene: microstructure,mechanical, thermal,and barrier properties

This effort reports on novel fluorinated polyamide (FPA) and polyamide 1010 (PA1010)-based blends and graphene reinforced nanocomposite. PA1010/FPA (80:20) blend was opted as matrix material on the basis of molecular weight, thermal, and shear stress performance. Graphene was obtained through in situ chemical method of graphene oxide reduction. PA1010/FPA/Graphene nanocomposites was developed using various graphene loadings (up to 5 wt.%). Thin film coatings were prepared on glass substrate. Consequently, the PA1010/FPA/Graphene attained regular spongy morphological pattern. PA1010/FPA/Graphene 3 also showed improved T₀ and T_max of 534 and 591 °C relative to the neat blend (T₁₀ 423 °C; T_max 551 °C). Limiting oxygen index measurement indicated better non-flammability of PA1010/FPA/Graphene 1–3 nanocomposite series (57–60%) relative to the blend series (28–31%). UL94 tests also showed V-0 rating for nanocomposites. Furthermore, PA1010/FPA/Graphene 3 nanocomposite revealed significantly high tensile strength (62 MPa), flexural modulus (1690 MPa), and adhesive properties to be utilized as coating materials. The nanocomposite coatings also displayed outstanding barrier properties against O₂ and H₂O compared with neat blends.     

Design and optimization of 2D photonic crystal waveguides based on silicon

The existence and properties of photonic band gaps was investigated for a square lattice of dielectric cylinders in air. Band structure calculations were performed using the transfer matrix method as function of the dielectric constant of the cylinders and the cylinder radius-to-pitch ratio r/a. It was found that band gaps exist only for transverse magnetic polarization for a dielectric contrast larger then 3.8 (index contrast >1.95). The optimum r/a ratio is 0.25 for the smallest index contrast. For silicon cylinders (n = 3.45) the widest gap is observed for r/a = 0.18. Band structure calculations as function of r/a show that up to four gaps open for the silicon structure. The effective index was obtained from the band structure calculations and compared with Maxwell–Garnett effective medium theory. Using the band structure calculations we obtained design parameters for silicon based photonic crystal waveguides. The possibility and limitations of amorphous silicon, silicon germanium and silicon-on-insulator structures to achieve index guiding in the third dimension is discussed.     

Morphology and Crystallization in Polystyrene/polyamide 6 Blends: Influence of a Reactive Compatibilizer and Nano-TiO2

A polystyrene (PS)/polyamide 6 (PA6) (70/30, weight ratio) blend in the presence of terminal malic anhydride functionalized PS (FPS) and nano-TiO₂ were prepared using a meltmixing technique. The morphology of the blend was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The crystallization behavior of the PA6 phase in the blend was studied using DSC techniques. The results showed that by adding 7.5 phr nano-TiO₂, the size of the dispersed PA6 domains was dramatically decreased; An additional 1.5 phr FPS to the PS/PA6/TiO₂ blend, for reactive blending, caused the size of the dispersed PA6 domain to become even smaller and more uniform, and a weak, broad crystallization exotherm of PA6 was observed. However, the degree of crystallinity of PA6 in PS/PA6/TiO₂/FPS blend was sharply increased.     

Effect of Filler Treatment on Crystallization,Morphology and Mechanical Properties of Polypropylene/Calcium Carbonate Composites

Pimelic acid (PA) was used as a new surface modifier for CaCO₃. The effects of PA treatment on the crystallization, morphology, and mechanical properties of PP/CaCO₃ composites were investigated. Fourier transform infrared (FTIR) spectroscopy analysis revealed that PA bonded to CaCO₃ and formed a calcium pimelate surface layer after reacting with CaCO₃. The results of wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and polarized light microscopy (PLM) proved that the PA treated CaCO₃ induced a large amount of β -iPP and decreased the spherulitic size of PP. The results of scanning electron microscopy (SEM) showed that the PA treatment enhanced the interfacial adhesion between the filler and the matrix, indicating the improvement of the compatibility between PP and CaCO₃. The toughness of the composites was improved by the more ductile β -form spherulites. When 1% of PA treated CaCO₃ was added, the notched impact strength reached its maximum, a value of 19.79 kJ/m², which was 3.64 times greater than that of the pure PP.     

Activation Energy for the Glass Transition of a Confined Elastomer in HDPE/PP Blends

Blends of two highly crystalline polymers containing an elastomer were prepared to study the glass transition of the confined elastomer. The polymers chosen were high density poly ethylene (HDPE), polypropylene (PP), and two elastomers of a different nature: natural number (NR) and EPDM. The dynamic mechanical analyzer (DMA) technique was used to analyze the storage modulus of blends with elastomer content from 0% to 30% by weight, with the remainder made up of equal amounts of HDPE and PP, and blends with 10% of the elastomer, but varied ratios of polyolefins. We used the differentiation modification of the Arrhenius method in the kinetic analysis assuming an n‐order relaxation mechanism, which allowed detecting the percolation threshold of NR. Results indicate that both temperature and activation energy for glass transition (T _g ) are dependent on the types of polymers in the blend and blend composition. The T _g and E values of the unblended elastomers are higher than those in blends; this behavior is associated with the elastomer confinement and blend morphology.     

Combustion of silane-nitrous oxide-argon mixtures: Analysis of laminar flame propagation and condensed products

The laminar burning rate, the explosion peak pressure, and the pressure rise coefficient have been measured for the first time for silane-nitrous oxide-argon mixtures using the spherically expanding flame technique in a constant volume combustion chamber. For these three parameters, the values obtained were higher than for hydrogen-nitrous oxide-argon and typical hydrocarbon-based mixtures. A maximum burning rate of 1800 g/m² s was measured at 101 kPa, whereas under similar conditions, a maximum burning rate around 950 g/m² s has been reported for hydrogen-nitrous oxide-argon mixtures. To better understand the chemical dynamics of flames propagating in SiH₄–N₂O–Ar mixtures, a detailed reaction model from the literature was improved using collision limit violation analysis and updated thermodynamic properties calculated with a high-level ab initio approach. The reaction model predicts the burning rate within 14% on average but demonstrates error close to 50% for the richest mixtures. The chemistry of the H–O–N system is important under all the conditions presently studied. The chemistry of the Si–H–O–N system demonstrates an increasing importance under rich conditions. In particular, the reactions (i) forming SiO_x(s); (ii) describing the interaction of Si-species with N₂O; and (iii) involving silicon hydrides, have an important role for the heat release dynamics. The condensed combustion products formed in the silane-nitrous oxide-argon flames were sampled and characterized using electron micrograph, electronic diffraction, energy-dispersive spectroscopy, and X-ray powder diffraction. For all equivalence ratios, silica spherical particles with a mean diameter in the range 200–300 nm were observed. In addition, for mixtures with Φ ≥ 2.2, silicon nanowires were formed. X-ray diffraction experiments showed that the silicon nanowires are composed of metal silicon characterized by a cubic structure (lattice parameter: a=5.425Å) with the Fm-3m space group.     

Rapid synthesis and characterization of silicon substituted nano hydroxyapatite using microwave irradiation

Nano sized hydroxyapatites with silicon substitution of three different silicon concentrations were successfully prepared first time by a rapid microwave assisted synthesis method, with a time saving and energy efficient technique. The effects of the Si substitution on crystallite size, particle size and morphology of the powders were investigated. The crystalline phase, microstructure, chemical composition, and morphology and particle size of hydroxyapatite and silicon substituted hydroxyapatites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and dynamic light scattering. The crystallite size and particle size decreases with increase in silicon content and particle morphology spheroidal for pure hydroxyapatite changes to elongated ellipsoidal crystals while silicon substitution increases. Fourier Transform Infrared Spectroscopy analysis reveals, the silicon incorporation to hydroxyapatite lattice occurs via substitution of silicate groups for phosphate groups. Substitution of phosphate group by silicate in the apatite structure results in a small increase in the lattice parameters in both a-axis and c-axis of the unit cell.     

Amorphous silicon hexaboride: a first-principles study

We report for the first time the atomic structure, electronic structure and mechanical properties of amorphous silicon hexaboride (a-SiB₆) based on first-principles molecular dynamics simulation. The a-SiB₆ model is generated from the melt and predominantly consists of pentagonal pyramid-like configurations and B₁₂ icosahedral molecules, similar to what has been observed in most boron-rich materials. The mean coordination number of B and Si atoms are 5.47 and 4.55, respectively. The model shows a semiconducting behaviour with a theoretical bandgap energy of 0.3?eV. The conduction tail states are found to be highly localised and hence the n-type doping is suggested to be more difficult than the p-type doping for a-SiB₆. The bulk modulus and Vickers hardness of a-SiB₆ are estimated to be about 118 and 13–17?GPa, respectively.     

Monoclinic symmetry in LaSrCu0.5Co0.5O4−z found by neutron,Guinier-and synchrotron-X-ray powder structure analysis

High resolution X-ray and neutron powder diffraction data of semiconducting LaSrCu_0.5Co_0.5O_3.7 have been collected in the temperature range of 5 to 300 K. A monoclinic structure with space groupI 2/m a=3.7952(1) Å,b=3.7902(1) Å,c=12.6507(1) Å, =90.074(1) Deg was refined with the Rietveld method for individual data sets as well as for the collection of all data simultaneously. The structureI 2/m results from an internal shearing of the octahedra and-unlikeCmca in superconducting La_1.85Sr_0.15CuO₄-not from a second order phase transition inI4/mmm. An alternative model with two tetragonal latticesa ₁=3.7902,a ₂=3.7952,c=12.6507 Å is discussed.     

Morphology and Mechanical Properties of Polyamide 6/Acrylonitrile-Butadiene-Styrene Blends Containing Carbon Nanotubes

The blends of polyamide 6/acrylonitrile-butadiene-styrene (PA6/ABS), with added styrene-maleic acid copolymer (SMA) compatibilizer, were prepared through melt mixing in an internal mixer. The effects of blend composition and various process conditions, as well as the addition of multi-wall carbon nanotubes (MWCNTs) to the blends, on the morphology and mechanical properties were investigated. The morphology of the blends and blend nanocomposites were observed by scanning electron microscopy (SEM) and analyzed using an image analysis technique. The mechanical behavior of the blends was investigated by tensile and also impact testing. The results showed that the blend composition as well as the processing conditions significantly affected the morphology and mechanical properties of the PA6/ABS blends. Among the various compositions, the blend with 36?wt.% of ABS and 4?wt.% of SMA compatibilizer exhibited the best mechanical properties. Comparing various speeds and times of mixing, it was found that less mixing speed and longer mixing times resulted in the favorable morphology and conditions for achievement of the desired toughness for the polyamide 6. By adding different amounts of MWCNTs to the blends, it was found that the presence of the carbon nanotubes changed the viscosity of the resulting nanocomposite and thus changed the morphology. These nanocomposites also showed an improvement in mechanical properties. The MWCNTs acted as a second compatibilizer, resulting in a synergistic effect on the mechanical properties of the PA6/ABS blend nanocomposites.