Thermal expansion of fumed silica/cyanate ester nanocomposites

The thermal expansion behavior of a cyanate ester matrix reinforced by fumed silica nanoparticles with average primary particle diameters of 12 and 40 nm was investigated with thermomechanical analysis. All nanocomposites showed decreased coefficients of thermal expansion (CTEs) in comparison with the neat bisphenol E cyanate ester resin, but the 12-nm fumed silica nanocomposites had lower CTEs than the 40-nm nanocomposites for equal volume fractions. The largest decrease in CTE was 27.0% for 20.7 vol % 40-nm fumed silica. When the data were compared to applicable theory, the best fit of the data was given by Schapery's upper limit and Shi's model. Estimates of the interphase volume fraction and effective thickness surrounding the nanoparticles were made with the results of Shi's model, and the results showed that the interphase volume fraction was larger for the 12-nm fumed silica nanocomposites, given an equal fraction of silica. The glass-transition temperature of the nanocomposites from thermomechanical analysis varied only slightly with the volume fraction. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of layer-aligned poly(vinyl alcohol)/graphene nanocomposites

Layer-aligned poly(vinyl alcohol)/graphene nanocomposites in the form of films are prepared by reducing graphite oxide in the polymer matrix in a simple solution processing. X-ray diffractions, scanning electron microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis are used to study the structure and properties of these nanocomposites. The results indicate that graphene is dispersed on a molecular scale and aligned in the poly(vinyl alcohol) (PVA) matrix and there exists strong interfacial interactions between both components mainly by hydrogen bonding, which are responsible for the change of the structures and properties of the PVA/graphene nanocomposites such as the increase in T_g and the decrease in the level of crystallization.     

Cycloolefin copolymer/fumed silica nanocomposites

We prepared cycloolefin copolymer (COC)/fumed silica nanocomposites by melt compounding to study the effect of the filler dimensions (filler surface area) on the physical properties, with particular attention to their thermal, mechanical, and optical behaviors. Thermogravimetric analysis revealed a positive contribution of silica nanoparticles to the thermal degradation resistance of COC, as the decomposition temperature of the nanofilled samples increased by 40°C with respect to that of the unfilled matrix. Dynamic mechanical thermal analysis and quasi‐static tensile tests of the nanocomposites evidenced a slight stiffening effect, proportional to the nanofiller surface area, without any reduction in the fracture toughness. Creep resistance of the nanocomposites was increased by the addition of silica nanoparticles, especially when high‐surface‐area nanoparticles were used. The positive effect of the nanoparticles on the viscoelastic and fracture behavior was related to the uniform dispersion of silica aggregates in the matrix. Ultraviolet–visible spectrometry measurements evidenced that the original transparency of neat COC was practically maintained after the addition of silica nanoparticles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermo-mechanical studies on Er3+-doped fluorophosphate glasses for near infrared lasers

Thermal, mechanical and thermo-mechanical properties of Mg(PO₃)₂-BaF₂-CaF₂-ErF₃ fluorophosphate (FP) glasses with varying Mg(PO₃)₂ and ErF₃ molar ratios have been investigated. The simultaneous thermal analysis revealed that the T_g, T_x, T_p and ΔT increased constantly with increasing Mg(PO₃)₂ and ErF₃ content and that favorable large values of ΔT (>100 °C) were obtained at higher Mg(PO₃)₂ and ErF₃ content. The thermo-mechanical analysis showed that the T_g and T_s increased constantly and coefficient of thermal expansion decreased from 16.5×10⁻⁶ K⁻¹ to 11.2^×10⁻⁶ K⁻¹ with an increase in Mg(PO₃)₂ and ErF₃ content. The Knoop hardness (H_K) increased constantly from 381 kgf/mm² to 480 kgf/mm² with increased Mg(PO₃)₂ and ErF₃ content, which indicates strengthening of the glass network with increased –PO bonds. The H_K measurement at different applied loads and indentation times was carried out and from this study, it was found that an appropriate incorporation of cations into the FP glasses and the optimum rare earth concentration could considerably increase the thermal and mechanical strength of the glass. The studied glass compositions showed beneficial thermal properties and outstanding mechanical strength and can be applied for fiber drawing.     

Creep resistant polymeric nanocomposites

In the present study, one of the unique improvements in polymer nanocomposites has been detected. Only with a very low volume fraction of inorganic nanoparticles, the creep resistance of thermoplastic could be significantly improved. 21 nm-TiO₂/PA6,6 nanocomposites were compounded using a twin-screw-extruder. The final specimens were formed using an injection-moulding machine. Static tension and tensile creep tests were carried out at room and an elevated temperature (50 °C). It was found out that the nanoparticles contributed to a remarkable reduction of the creep rate under various constant loads at both temperature levels. It is assumed that the nanoparticles restrict the slippage, reorientation and motion of polymer chains. In this way, they influence the stress transfer on a nanoscale, which finally results in these improvements.     

Development and characterization of novel DOPO based phosphorus tetraglycidyl epoxy nanocomposites for aerospace applications

A study was made in the present investigation on the development and characterization of 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) based phosphorus tetraglycidyl epoxy nanocomposites and to find its suitability for use in aerospace and high performance applications. Phosphorus-containing diamine (DOPO-NH₂) was synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 4,4′-diaminobenzophenone (DABP), and this is utilized for the preparation of DOPO based phosphorus containing tetraglycidyl epoxy denoted as ‘D’. The synthesized resin was characterized by Fourier transform infrared spectra (FT-IR) and ¹H, ¹³C nuclear magnetic resonance (NMR) spectra. Nanoclay and polyhedral oligomeric silsesquioxane (POSS)-amine nano-reinforcements denoted as N1 and N2 were incorporated into the synthesized epoxy resin. Curing was done with diaminodiphenylmethane (DDM) and bis(3-aminophenyl) phenylphosphine oxide (BAPPO) curing agents denoted as X and Y respectively. Mechanical, thermal, flame retardant, water absorption behaviour and electrical properties of the epoxy nanocomposites were studied and the results are discussed.     

Preparation and characterization of exfoliated layered double hydroxide/silicone rubber nanocomposites

Silicone rubber (SR)/Mg–Al layered double hydroxide (LDH) nanocomposites were prepared by the solution intercalation of SR crosslinked by a platinum‐catalyzed hydrosilylation reaction into the galleries of dodecyl sulfate intercalated layered double hydroxide (DS–LDH). X‐ray diffraction and transmission electron microscopy analysis showed the formation of exfoliated structures of organomodified LDH layers in the SR matrix. The tensile strength and elongation at break of SR/DS–LDH (5 wt %) were maximally improved by 53 and 38%, respectively, in comparison with those of the neat polymer. Thermogravimetric analysis indicated that the thermal degradation temperature of the exfoliated SR/DS–LDH (1 wt %) nanocomposites at 50% weight loss was 20°C higher than that of pure SR. Differential scanning calorimetry analysis data confirmed that the melting temperature of the nanocomposites increased at lower filler loadings (1, 3, and 5 wt %), whereas it decreased at a higher filler loading (8 wt %). The relative improvements in the solvent‐uptake resistance behavior of the SR/DS–LDH nanocomposites were also observed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and characterization of graphene/poly(vinyl alcohol) nanocomposites

Graphene (GE)‐based nanocomposites are emerging as a new class of materials that hold promise for many applications. In this article, we present a general approach for the preparation of GE/poly(vinyl alcohol) (PVA) nanocomposites. The basic strategy involved the preparation of graphite oxide from graphite, complete exfoliation of graphite oxide into graphene oxide sheets, followed by reduction to GE nanosheets, and finally, the preparation of the GE/PVA nanocomposites by a simple solution‐mixing method. The synthesized products were characterized by X‐ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, and differential scanning calorimetry analysis. The GE nanosheets were well dispersed in the PVA matrix, and the restacking of the GE sheets was effectively prevented. Because of the strong interfacial interaction between PVA and GE, which mainly resulted from the hydrogen‐bond interaction, together with the improvement in the PVA crystallinity, the mechanical properties and thermal stability of the nanocomposites were obviously improved. The tensile strength was increased from 23 MPa for PVA to 49.5 MPa for the nanocomposite with a 3.25 wt % GE loading. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of particle size and grafting density on the mechanical properties of polymer nanocomposites

End-grafting polymer chains to nanoparticles in polymer nanocomposite is a widely used method to disperse inorganic particles in a polymeric matrix in order to improve the material properties. While many fundamental studies have investigated how various factors influence the dispersion or aggregation of the nanoparticles, the effect of grafting on the resulting material properties has received considerably less attention. In particular, the effect of nanoparticle curvature and grafting density on the mechanical properties in polymer nanocomposites remains elusive. In this study, we develop a coarse-grained model of a polymer glass containing grafted nanoparticles and examine the resulting effects on the mechanical properties. By carefully designing the parameters of our polymer nanocomposites model, we can maintain dispersion of the nanoparticles whether they are grafted with polymer chains or not, which allows us to isolate the effect of end-grafting on the resulting mechanical properties. We examine how the nanoparticle size and grafting density affect the elastic constants, strain hardening modulus, as well as the mobility of the polymer segments during deformation. We find that the elastic constants and yield properties are enhanced nearly uniformly for all of our nanocomposite systems, while the strain hardening modulus depends weakly on the grafting density and the nanoparticle size.     

Preparation and characterization of epoxy/kaolinite nanocomposites

Epoxy/kaolinite nanocomposites were prepared by adding the organically modified layered kaolinite to an epoxy resin [biphenyl phenol novolac epoxy resin (BPNE)] with 4,4′‐diamino biphenyl sulfone (DDS) as a curing agent. The dispersion state of the kaolinite within crosslinked epoxy‐resin matrix was examined by X‐ray diffraction (XRD) and transmission electron micrograph (TEM). The effects of kaolinite on thermal properties were investigated and discussed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Experimental results show that BPNE/kaolinite nanocomposites exhibit improved thermal than pure BPNE. When the kaolinite content is 5 wt %, the BPNE/kaolinite nanocomposites show the best thermal properties. These results indicate that nanocomposition is an efficient and convenient method to improve the thermal properties of BPNE. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of poly(vinyl alcohol) nanocomposites made from cellulose nanofibers

A method using a combination of ball milling, acid hydrolysis, and ultrasound was developed to obtain a high yield of cellulose nanofibers from flax fibers and microcrystalline cellulose (MCC). Poly(vinyl alcohol) (PVA) nanocomposites were prepared with these additives by a solution‐casting technique. The cellulose nanofibers and nanocomposite films that were produced were characterized with Fourier transform infrared spectrometry, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. Nanofibers derived from MCC were on average approximately 8 nm in diameter and 111 nm in length. The diameter of the cellulose nanofibers produced from flax fibers was approximately 9 nm, and the length was 141 nm. A significant enhancement of the thermal and mechanical properties was achieved with a small addition of cellulose nanofibers to the polymer matrix. Interestingly, the flax nanofibers had the same reinforcing effects as MCC nanofibers in the matrix. Dynamic mechanical analysis results indicated that the use of cellulose nanofibers (acid hydrolysis) induced a mechanical percolation phenomenon leading to outstanding and unusual mechanical properties through the formation of a rigid filler network in the PVA matrix. X‐ray diffraction showed that there was no significant change in the crystallinity of the PVA matrix with the incorporation of cellulose nanofibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and characterization of carbon nanofiber reinforced thermoplastic polyurethane nanocomposites

The effect of CNFs on hard and soft segments of TPU matrix was evaluated using Fourier transform infrared (FTIR) spectroscope. The dispersion and distribution of the CNFs in the TPU matrix were investigated through wide angle X‐ray diffraction (WAXD), field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), polarizing optical microscope (POM), and atomic force microscope (AFM). The thermogravimetric analysis (TGA) showed that the inclusion of CNF improved the thermal stability of virgin TPU. The glass transition temperature (T_g), crystallization, and melting behaviors of the TPU matrix in the presence of dispersed CNF were observed by differential scanning calorimetry (DSC). The dynamic viscoelastic behavior of the nanocomposites was studied by dynamical mechanical thermal analysis (DMTA) and substantial improvement in storage modulus (E') was achieved with the addition of CNF to TPU matrix. The rheological behavior of TPU nanocomposites were tested by rubber processing analyzer (RPA) in dynamic frequency sweep and the storage modulus (G') of the nanocomposites was enhanced with increase in CNF loading. The dielectric properties of the nanocomposites exhibited significant improvement with incorporation of CNF. The TPU matrix exhibits remarkable improvement of mechanical properties with addition of CNF. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermo-mechanical characterization of plasticized PLA: Is the miscibility the only significant factor?

PLA is a widely used polymer which has received much attention in the last decade because of its originating from renewable resources and its potential biodegradability. PLA fulfils the packaging industry's requirements for most of the rigid objects but the polymer needs to be plasticized to be used as soft films. In this work, agreed plasticizers for food contact were melt mixed with L-PLA and then, the glass transition, melting, crystallization and mechanical properties of the blends were investigated. The experimental results were compared to the predicted results found through empirical interaction parameters and Fox equations. Molecular scale miscibility is assumed in the amorphous phase whatever the plasticizer. The mobility gained by the PLA chains in the plasticized blends yields crystallization, which is the driving force for various scale phase separations.     

Mechanical and optical properties of clay-based nanocomposites coatings for wood flooring

Clay-based nanocomposites coatings cured by UV light were prepared by four different types of dispersion equipment: a high-speed mixer, a ball mill, a bead mill and a three-roll mill. For each treatment, formulations were prepared at 1, 3 and 10 wt% of clay. A previous study had established the dispersion efficiency of each treatment and the effect of clay dispersion on UV curing. The present study relates to the effect of clay dispersion on mechanical and optical properties. The mechanical properties studied included abrasion resistance, direct and reverse impact resistance as well as Persoz hardness. Optical properties, such as haze, gloss, color and optical clarity were assessed. An analysis of variance (ANOVA) was conducted to evaluate the effect of clay loading and process type on mechanical and optical properties. A statistical analysis revealed that each property varied with the percentage of clay loading in every treatment. It was found that the quality of the clay dispersion strongly affected both mechanical and optical properties.     

聚苯胺/镍纳米复合材料的制备及其表征

以苯胺（An）、氯化镍（NiCl2×6H2O）为原料,原位聚合法合成聚苯胺/镍纳米复合微粒。采用X射线衍射仪、扫描电镜、傅里叶变换红外光谱仪、振动样品磁强计（VSM）及四探针测试仪技术表征了复合微粒的结构、形貌和电磁性能。结果表明：复合微粒在室温外加磁场下表现出铁磁性物质具有的磁滞现象,饱和磁化强度为9.44 emu/g,复合微粒在室温下的电导率为5×10-3 S/cm。     

Predictions of micromechanics models for interfacial/interphase parameters in polymer/metal nanocomposites

In this paper, the polymer-metal interfacial/interphase parameters (PMIP) in polymer/metal nanocomposites are studied by modeling the mechanical properties. In this regard, the experimental results of yield strength, Young's modulus and elongation at break can be compared with the micromechanical models to evaluate the PMIP. The good agreement obtained between the experimental data of samples and the predictions confirms the applicability of models for polymer/metal nanocomposites. Many calculated parameters show the existence of a strong interphase in the reported samples. It is concluded that the fine morphology of nanoparticles and the strong interaction/adhesion at the polymer-metal interface can produce the significant PMIP in the polymer/metal nanocomposites.     

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.     

On the importance of specific interface area in clay nanocomposites of PMMA filled with synthetic nano-mica

In clay nanocomposites, the specific interface area is the key factor determining potential improvements of properties. Nevertheless, in most systematic studies of nanocomposites little emphasis is put on assuring and characterizing dispersion quality. To probe the influence of dispersion quality, we compare nanocomposites filled with two layered silicates which were made by melt compounding and solution blending, respectively. Poly(methyl methacrylate) (PMMA) is chosen here as a thermoplastic model matrix which was compounded with a synthetic nano-mica (O-hect) and commercial Bentone with typical diameters of 5–7 μm and <300 nm, respectively.     

Preparation and Characterization of Polypropylene Nanocomposites Filled with Nano Calcium Phosphate

The synthesized nano calcium phosphate by matrix mediated growth and controlled technique was used as nanofiller in the preparation of polypropylene nanocomposites. Nanocomposites with different filler concentrations were prepared. The content of nano calcium phosphate was varied from 1 to 3 wt% in the preparation of PP nanocomposites. During preparation of nanocomposites shear rate was varied by means of increase in rpm, i.e., 60, 70, 80 and 90 with the help of Brabender Plastograph and the effect of shear rate was studied with respective to mechanical and thermal properties of composites. The comprehensive evaluation of the PP nanocomposites filled with nano calcium phosphate was done to observe the substantial improvement in the performance properties. The mechanical and thermal properties were determined by Universal Testing Machine (UTM) and Thermogravimetric Analyzer (TGA), respectively. The morphology of the fracture surfaces of the prepared PP nanocomposites filled with nano calcium phosphate was studied by Scanning Electron Microscopy (SEM).     

Synthesis and characterization of linear low‐density polyethylene/sepiolite nanocomposites

Linear low‐density polyethylene (LLDPE)/sepiolite nanocomposites were prepared by melt blending using unmodified and silane‐modified sepiolite. Two methods were used to modify sepiolite: modification before heat mixing (ex situ) and modification during heat mixing (in situ). The X‐ray diffraction results showed that the position of the main peak of sepiolite remained unchanged during modification step. Infrared spectra showed new peaks confirming the development of new bonds in modified sepiolite and nanocomposites. SEM micrographs revealed the presence of sepiolite fibers embedded in polymer matrix. Thermogravimetric analysis showed that nanocomposites exhibited higher onset degradation temperature than LLDPE. In addition, in situ modified sepiolite nanocomposites exhibited higher thermal stability than ex situ modified sepiolite nanocomposites. The ultimate tensile strength and modulus of the nanocomposites were improved; whereas elongation at break was reduced. The higher crystallization temperature of some nanocomposite formulations revealed a heterogeneous nucleation effect of sepiolite. This can be exploited for the shortening of cycle time during processing. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012