Mechanical and physical properties of epoxy composites reinforced by vapor grown carbon nanofibers

Epoxy/vapor grown carbon nanofiber composites (VGCF) with different proportions of VGCF were fabricated by the in situ process.The VGCFs were well dispersed in both of the low and high viscosity epoxy matrices, although occasional small aggregates were observed in a high viscosity epoxy of 20 wt.%. The dynamic mechanical behavior of the nanocomposite sheets was studied. The storage modulus and the glass transition temperature (T_g) of the polymer were increased by the incorporation of VGCFs.The electrical and mechanical properties of the epoxy-VGCFs nanocomposite sheets with different weight percentages of VGCFs were discussed. The results were that both had maximum tensile strength and Young’s modulus at 5 wt.% for both materials and reduced the fracture strain with increasing filler content. The electrical resistivity was decreased with the addition of filler content. Mechanical, electrical and thermal properties of low viscosity epoxy composites were resulted better than that of the high viscosity composites.     

Influence of nanosilica particles on the cure and physical properties of an epoxy thermoset resin

Measurements are reported on the cure and physical properties of an epoxy resin created using a functionalised nanosilica filler. The filled bisphenol A epoxy (Nanopox A410) contained 40 wt% silica nanoparticles and was blended with two bisphenol A resins of molecular weights of 355 and 1075 g mol^?1, respectively. Cure was achieved using 3,3‐diaminodiphenylsulfone. The functionality of the mixture containing the epoxy nanoparticles was determined using NMR analysis. Cure times showed a progressive decrease with increasing silica level. Dynamic mechanical thermal analysis showed a decrease in the value of the glass transition temperature (T_g) with increasing silica level. T_g was further studied using differential scanning calorimetry. The ability of the nanosilica to create a stable network structure was demonstrated by the variation of the high‐temperature modulus with silica composition. Thermomechanical analysis carried out below and above T_g showed a progressive decrease in the expansion coefficients with increasing silica level, indicating the effectiveness of the functionalised silica nanoparticles in forming a network. The network formed during cure in the nano‐modified epoxy is unable to undergo the densification possible in the pure resin material and explains the observed lowering of T_g with increasing nanosilica content. Copyright © 2009 Society of Chemical Industry     

Film‐forming behavior and mechanical properties of colloidal silica/polymer latex blends with high silica load

In this article, silica sol (diameter: 8–100 nm) and polymer latex (T_g < 25°C) were mixed and dried at room temperature to prepare nanocomposite films with high silica load (≥50 wt %). Effects of silica size, silica load, and the T_g of the polymer on the film‐forming behavior of the silica/polymer latex blend were investigated. The transparency, morphology, and mechanical properties of the nanocomposite films were examined by UV–Vis spectroscopy, SEM, and nanoindentation tests, respectively. Transparent and crack‐free films were produced with silica loads as high as 70 wt %. Thirty nanometers was found to be the critical silica size for the evolution of film‐forming behavior, surface morphology, and mechanical properties. Colloidal silica particles smaller than this critical size act as binders to form strong silica skeleton. This gives the final silica/polymer nanocomposite film its porous surface and high mechanical strength. However, silica particles with sizes of 30 nm or larger tend to work as nanofillers rather than binders, causing poor mechanical strength. We also determined the critical silica load appeared for the mechanical strength of silica/polymer film at high silica load. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A new extra situ sol–gel route to silica/epoxy (DGEBA) nanocomposite. A DTA study of imidazole cure kinetic

Silica nanoparticles were obtained through the Stöber method, from mixtures of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTS). The nanoparticles were dispersed in tetrahydrofuran (THF) and coupled to bisphenol A epoxy resin (DGEBA) through surface amino groups. After removing THF non-isothermal cure was performed at different heating rates (2–20°C/min), using imidazole (2–4 wt%) as curing agent. For the sake of comparison bare DGEBA epoxy polymers were also prepared with similar schedule A nanocomposite of well-dispersed silica nanoparticles (5 wt%) in a fully cured epoxy matrix was easily obtained. Lower cure kinetics were observed with silica addition. This was attributed to reduction of the imidazole volume concentration. Cure activation energy was not influenced by silica presence, whereas it changed with the imidazole content. Therefore, experimental results suggested that silica had only an indirect effect (the reduction of the imidazole molar concentration) on the epoxy matrix cure kinetics. Glass transformation temperatures, T _g, as high as 175°C were recorded. The nanocomposite glass transformation temperature depended on the heating rate of the cure process, the imidazole and silica content. T _g changes as high as 40°C were detected as a function of the heating rate. At higher imidazole content no differences in T _g values between bare polymer and the nanocomposite were observed. This suggests that a higher imidazole content assures a better interconnection between the compatibilizing epoxy shell around the nanoparticles and the epoxy matrix. The new proposed methodology is an easy route to engineer both nanocomposites structure and interfacial interactions, thus tailoring their properties.     

Synthesis and properties of waterborne epoxy acrylate nanocomposite coating modified by MAP-POSS

In this paper, waterborne epoxy acrylate (EA) coating modified with methylacryloylpropyl polyhedral oligomeric silsesquioxanes (MAP-POSS) was prepared. The cure kinetics of the coating was investigated by differential scanning calorimetry (DSC). The curing process, thermal and mechanical properties of the coating were investigated by FTIR, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). These results show that the non-isothermal curing process can be described by Kissinger method and a two-parameter autocatalytic Šesták–Berggren (S–B) model. The kinetic equations of curing reaction were obtained. The UV-curing property of MAP-POSS/EA nanocomposite coating is better than that of pure epoxy acrylate system. The glass transition temperature (T_g) increases with increasing MAP-POSS content. When MAP-POSS content is 12 wt%, the T_g reaches the maximum 54.3 °C which is 9.5 °C higher than that of pure epoxy acrylate.     

Electrical properties of a composite comprising epoxy resin and α-hematite nanorods

Electrical properties of pure epoxy and epoxy-hematite nanorod composites have been investigated. The nanorods were synthesized by the forced hydrolysis method and further mixed with epoxy to obtain the nanocomposite. TEM analysis revealed that they have an average diameter of about 8 nm, with an average aspect ratio of 25. DC-conductivity and DC-current relaxation measurements showed a significant influence of Fe₂O₃ nanorods on the DC-electrical properties of the epoxy matrix. However, the observed effects of the filler below and above the glass transition are different. Because of their high specific surfaces, nanorods affected segmental mobility of epoxy molecules to a large extent, which resulted in an increase in the glass transition temperature (T_g) and a decrease in the real part of dielectric permittivity in high frequency/low temperature region. It is further observed that at elevated temperatures (above T_g) and low frequencies the real part of dielectric permittivity of the nanocomposite exceeds that of the pure matrix, i.e. there is a transition towards microcomposite-like dielectric behaviour.     

Poly (styrene‐n‐butyl acrylate‐methyl methacrylate)/silica nanocomposites prepared by emulsion polymerization

Poly (styrene‐n‐butyl acrylate‐methyl methacrylate) (PSBM)/silica nanocomposite was prepared by emulsion polymerization in the presence of oleic acid surface modified nanosilica. The structure, morphology, size, and size distribution were characterized by Fourier transform infrared (FTIR), transmission electron microscopy (TEM), and dynamics laser scattering. The chemical bond was formed between PSBM and nanosilica revealed by FTIR and TEM studies. The composite particles with an averaged diameter ranging from 30 to 80 nm have the core‐shell structure. The effect of silica content on the glass transition temperature T_g, pyrolyze temperature, and rheological behavior of PSBM composites was systematically investigated. The results indicated that the addition of nanosilica could effectively inhibit chain movement, and improved the pyrolyze temperature of PSBM. The steady viscosity and dynamic modulus were strongly dependent on the content and distribution of nanosilica in PSBM nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The mechanisms and mechanics of the toughening of epoxy polymers modified with silica nanoparticles

The present paper considers the mechanical and fracture properties of four different epoxy polymers containing 0, 10 and 20 wt.% of well-dispersed silica nanoparticles. Firstly, it was found that, for any given epoxy polymer, their Young’s modulus steadily increased as the volume fraction, v_f, of the silica nanoparticles was increased. Modelling studies showed that the measured moduli of the different silica-nanoparticle filled epoxy polymers lay between upper-bound values set by the Halpin-Tsai and the Nielsen ‘no-slip’ models, and lower-bound values set by the Nielsen ‘slip’ model; with the last model being the more accurate at relatively high values of v_f. Secondly, the presence of silica nanoparticles always led to an increase in the toughness of the epoxy polymer. However, to what extent a given epoxy polymer could be so toughened was related to structure/property relationships which were governed by (a) the values of glass transition temperature, T_g, and molecular weight, M_c, between cross-links of the epoxy polymer, and (b) the adhesion acting at the silica nanoparticle/epoxy-polymer interface. Thirdly, the two toughening mechanisms which were operative in all the epoxy polymers containing silica nanoparticles were identified to be (a) localised shear bands initiated by the stress concentrations around the periphery of the silica nanoparticles, and (b) debonding of the silica nanoparticles followed by subsequent plastic void growth of the epoxy polymer. Finally, the toughening mechanisms have been quantitatively modelled and there was good agreement between the experimentally-measured values and the predicted values of the fracture energy, G_c, for all the epoxy polymers modified by the presence of silica nanoparticles. The modelling studies have emphasised the important roles of the stress versus strain behaviour of the epoxy polymer and the silica nanoparticle/epoxy-polymer interfacial adhesion in influencing the extent of the two toughening mechanisms, and hence the overall fracture energy, G_c, of the nanoparticle-filled polymers.     

Study on structure and properties of SSBR/SiO2 co‐coagulated rubber and SSBR filled with nanosilica composites

The morphological structure, glass transition, mechanical properties, and dynamic mechanical properties of star‐shaped solution‐polymerized styrene‐butadiene rubber (SSBR) synthesized by a multifunctional organic lithium initiator and SiO₂‐SSBR composite (N‐SSBR) prepared through adding a small amount of nanosilica modified by silane coupling agent to star‐shaped SSBR synthetic solution and co‐coagulating, and their nanocomposites filled with 20 phr nanosilica were investigated, respectively. The results showed that the silica particles were well dispersed with nanosize in N‐SSBR, which glass‐transition temperature (T_g) was 2°C higher than SSBR. N‐SSBR/SiO₂ nanocomposite exhibited lower Payne effect and internal friction loss, higher mechanical properties, and its T_g was 2°C higher than SSBR/SiO₂ nanocomposite. N‐SSBR might promote the dispersion of nanosilica powder in matrix and could be applied to green tire tread materials. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermo-mechanical behaviors and moisture absorption of silica nanoparticle reinforcement in epoxy resins

An investigation of the thermo-mechanical behavior of silica nanoparticle reinforcement in two epoxy systems consisting of diglycidyl ether of bisphenol F (DGEBF) and cycloaliphatic epoxy resins was conducted. Silica nanoparticles with an average particle size of 20 nm were used. The mechanical and thermal properties, including coefficient of thermal expansion (CTE), modulus (E), thermal stability, fracture toughness (K_IC), and moisture absorption, were measured and compared against theoretical models. It was revealed that the thermal properties of the epoxy resins improved with silica nanoparticles, indicative of a lower CTE due to the much lower CTE of the fillers, and furthermore, DGEBF achieved even lower CTE than the cycloaliphatic system at the same wt.% filler content. Equally as important, the moduli of the epoxy systems were increased by the addition of the fillers due to the large surface contact created by the silica nanoparticles and the much higher modulus of the filler than the bulk polymer. In general, the measured values of CTE and modulus were in good agreement with the theoretical model predictions. With the Kerner and Halpin-Tsai models, however, a slight deviation was observed at high wt.% of fillers. The addition of silica nanoparticles resulted in an undesirable reduction of glass transition temperature (T_g) of approximately 20 °C for the DGEBF system, however, the T_g was found to increase and improve for the cycloaliphatic system with silica nanoparticles by approximately 16 °C. Furthermore, the thermal stability improved with addition of silica nanoparticles where the decomposition temperature (T_d) increased by 10 °C for the DGEBF system and the char yield significantly improved at 600 °C. The moisture absorption was also reduced for both DGEBF and cycloaliphatic epoxies with filler content. Lastly, the highest fracture toughness was achieved with approximately 20 wt.% and 15 wt.% of silica nanoparticles in DGEBF and cycloaliphatic epoxy resins, respectively.     

Structure and properties of polyurethane/nanosilica composites

Nanosilica particles were directly introduced into polyester polyol resins through in situ polymerization and blending methods, then cured by isophorone diisocyanate (IPDI) trimers to obtain nanocomposite polyurethanes. FTIR and TGA analyses indicated that more polyester segments had reacted with silica particles during in situ polymerization than during the blending method, accompanied by higher T_g and more homogeneous dispersion of nanosilica particles in the polymer matrix from in situ polymerization. Maximum values in T_g, tensile properties, macrohardness, abrasion resistance, and UV absorbance were obtained when the particle size of silica was about 28 nm. The polyurethane/nanosilica composites obtained by in situ polymerization generally had better mechanical properties than those by the blending method except for some unexpected macrohardness at relatively high silica content. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1032–1039, 2005     

PMMA-mesocellular foam silica nanocomposites prepared through batch emulsion polymerization and compression molding

PMMA-mesoporous silica nanocomposites were prepared for the first time through in situ batch emulsion polymerization of methyl methacrylate in the presence of large pore MSU-F silica with a mesocellular foam structure (24.8 nm average cavity size) and subsequent compression molding of the polymer-silica nanoparticle mixtures. For composites containing 5.0 wt % silica, the onset decomposition temperature and the temperature at 10% weight loss for the nanocomposite increased 41 °C and 50 °C, respectively, in comparison to pure PMMA. The glass transition temperature of the nanocomposite increased 9.3 °C, as determined by differential scanning calorimetry. In addition, the storage modulus determined by dynamic mechanical analysis increased 17% and 80% at 50 °C and 100 °C, respectively. Substantial improvements in tensile strength (+50%) and modulus (+72%), were achieve at 10 wt % nanoparticle loading. Composites made by compression molding of physical mixtures of PMMA and MSU-F silica powders provide less improvement in thermal stability, glass transition temperature and mechanical properties in comparison to the composites made through in situ batch emulsion polymerization. Unlike previously reported composites made from nanoclays, the silica composites reported here show improvements in both thermal stability and mechanical reinforcement.     

Enhancement of dynamic mechanical properties and flame resistance of nanocomposites based on epoxy and nanosilica modified with KR-12 coupling agent

The epoxy/silica nanocomposites containing a wide range of isopropyltri[di(octyl) phosphate] titanate coupling agent (KR-12) modified nanosilica (m-nanosilica) loading (0–7 wt%) cured with tetrabutyl titanate hardener were prepared. Their morphology, thermal stability, thermal expansion, and mechanical properties including hardness, abrasion resistance were investigated. The wetting ability of epoxy-nanosilica systems on glass surface was assessed based on static contact angle. The obtained results showed that the contact angle of the nanocomposites containing m-nanosilica is slightly changed as compared to the contact angle of pure epoxy resin and lower than that of the nanocomposite containing unmodified nanosilica. The data of dynamic mechanical analysis of the nanocomposites using different nanosilica content indicated that the presence of m-nanosilica lowered the recovery energy of the nanocomposites to 41.62% as compared to neat epoxy. The limiting oxygen index (LOI) of the nanocomposites confirmed that the m-nanosilica increased the flame retardance of epoxy matrix. When using 7 wt% of m-nanosilca, the LOI value of the nanocomposite was 27.4 while this index of neat epoxy was 21.6. The scanning electron microscopic images of residual char combustion of the nanocompsites indicated a formation of nanosilica layer contributed to restrain combustion of the material.     

A study on the anticorrosion performance of the epoxy-polyamide nanocomposites containing ZnO nanoparticles

Epoxy nanocomposites were prepared using different loadings (2, 3.5, 5 and 6.5 wt%) of ZnO nanoparticles. Nanocomposites were applied on steel substrates. Samples were immersed in 3.5 wt% NaCl solution for 1344 h. Corrosion resistance of the coatings was studied by an electrochemical impedance spectroscopy (EIS). The effects of addition of nanoparticles on the mechanical properties of the epoxy coating were studied by a dynamic mechanical thermal analysis (DMTA). Curing behavior of the coatings containing nanoparticles was studied by a differential scanning calorimeter (DSC). Atomic force microscope (AFM) was utilized to investigate the surface topography and surface morphology of the coatings. Coating resistance against hydrolytic degradation was studied by FTIR (Fourier Transform Infrared).Results showed that addition of low loadings of nanoparticles can increase T_g of the composite. Decrease in T_g and cross-linking density of the coating were observed at high loadings of nanoparticles. It was found that nanoparticles can influence the curing behavior of the epoxy coating. Nanoparticles improved the corrosion resistance of the epoxy coating. Increase in coating resistance against hydrolytic degradation was obtained using nanoparticles.     

Investigation of accelerated aging behaviour of high performance industrial coatings by dynamic mechanical analysis

Dynamic mechanical analysis (DMA) represents one of the most important methods for understanding mechanical behaviour of surface coatings providing a valuable link between chemistry, morphology, and performance properties. In this work, dynamic mechanical properties of several high performance industrial coatings were studied extensively. Four commercially available topcoats namely alkyd modified polyurethane (PU), economy aliphatic PU, high performance aliphatic PU and epoxy modified polysiloxane were selected based on their cure chemistries, volume solids, and overall performance. DMA was used to determine elastic modulus, glass transition temperature (T_g), crosslink density and creep behaviour of these coatings. DMA data were substantiated with mechanical and performance properties. Among the coatings, epoxy modified polysiloxane showed the highest T_g of 65.6 °C as well as crosslink density value of 2.24 × 10⁻³ mol/cc which was attributed to its superior mechanical and performance properties. In addition, topcoats were also subjected to artificial aging process in accelerated cyclic corrosion cabinet and QUV-weatherometer, respectively. The consequent changes in their physico-mechanical properties post exposure were also evaluated using DMA and correlated with other performance properties. After aging, the T_g increased substantially for all the coatings irrespective of their exposure type. For example, T_g of economy aliphatic PU increases from 38.4 °C to 52.9 °C and 51 °C after cyclic corrosion and UV-B weathering, respectively. However, crosslink densities either increased or decreased depending on the type of exposure and cure chemistries. These changes were corroborated using the Fourier transform infrared spectroscopy findings. The outcome of this study is expected to generate new insights into the behaviour of these coatings under dynamic mechanical stress and its relation with long term performance properties.     

Studies on syntheses and properties of novel CeO2/polyimide nanocomposite films from Ce(Phen)3 complex

A series of cerium dioxide (CeO₂)/polyimide (PI) nanocomposites were successfully prepared from Ce(Phen)₃ and polyamic acid (PAA) via the solution direct-dispersing method, followed by a step thermal imidization process. TGA and XPS studies showed that the cerium complex decomposed to form CeO₂ during the thermal imidization process at 300 °C. SEM observation showed that the formed CeO₂ as nanoparticles was well dispersed in polyimide matrix with a size of about 50-100 nm for samples with different contents of CeO₂. Thermal analysis indicated that the introduction of CeO₂ decreased the thermal stability of nanocomposite films due to the decomposition of Ce(Phen)₃ in the imidization process, while the glass transition temperature (T_g) increased obviously, especially nanocomposite films with high loading of CeO₂ exhibited a trend of disappearance of T_g. DMTA and static tensile measurements showed that the storage modulus of nanocomposite films increased, while the elongation at break decreased with increasing CeO₂ content.     

Facile tailoring of thermal transition temperatures of epoxy shape memory polymers

A critical parameter for a shape memory polymer (SMP) lies in its shape memory transition temperature. For an amorphous SMP polymer, it is highly desirable to develop methods to tailor its T_g, which corresponds to its shape memory transition temperature. Starting with an amine cured aromatic epoxy system, epoxy polymers were synthesized by either reducing the crosslink density or introducing flexible aliphatic epoxy chains. The thermal and thermomechanical properties of these epoxy polymers were characterized by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). All the crosslinked epoxy polymers with T_g's above room temperature were found to possess shape memory properties. Overall, our approach represents a facile method to precisely tune the T_g of epoxy SMP polymers ranging from room temperature to 89 °C.     

A simple approach to fabricate morphological gradient on polymer surfaces

This paper presents a novel and feasible approach for fabrication of morphological gradient surfaces based on the film-formation of nanocomposite polymer latex. In this method, when the polymer latex with relatively low glass transition temperature (T_g) was blended with colloidal silica and then dried at certain temperatures, a morphological evolution with deeper pores from the center to the edge could be directly obtained on polymer surface. Neither careful control of experimental conditions nor any complex processes are needed. The T_g of polymer, the silica content, the solvent and the drying temperature have significant influences on this surface morphology. The film-formation mechanisms at different drying temperatures are also discussed.     

Enhanced cycling performance of Fe3O4-graphene nanocomposite as an anode material for lithium-ion batteries

Fe₃O₄-graphene nanocomposite was prepared by a gas/liquid interface reaction. The structure and morphology of the Fe₃O₄-graphene nanocomposite were characterized by X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The electrochemical performances were evaluated in coin-type cells. Electrochemical tests show that the Fe₃O₄-22.7 wt.% graphene nanocomposite exhibits much higher capacity retention with a large reversible specific capacity of 1048 mAh g⁻¹ (99% of the initial reversible specific capacity) at the 90th cycle in comparison with that of the bare Fe₃O₄ nanoparticles (only 226 mAh g⁻¹ at the 34th cycle). The enhanced cycling performance can be attributed to the facts that the graphene sheets distributed between the Fe₃O₄ nanoparticles can prevent the aggregation of the Fe₃O₄ nanoparticles, and the Fe₃O₄-graphene nanocomposite can provide buffering spaces against the volume changes of Fe₃O₄ nanoparticles during electrochemical cycling.     

Intercalation and exfoliation behavior of epoxy resin/curing agent/montmorillonite nanocomposite

The epoxy resin/curing agent/montmorillonite nanocomposite was prepared by a casting and curing process. The intercalation and exfoliation behaviors of epoxy resin in the presence of organophilic montmorillonite were investigated by X‐ray diffraction (XRD) and dynamic mechanical thermal analysis (DMTA). For the diethylenetriamine curing agent, the intercalated nanocomposite was obtained; and the exfoliated nanocomposite would be formed for tung oil anhydride curing agent. The curing condition does not affect the resulting kind of composite, both intercalation or exfoliation. For intercalated nanocomposite, the glass transition temperature T_g, measured by DMTA and affected by the curing temperature of matrix epoxy resin is corresponded to that of epoxy resin without a gallery. The α′ peak of the loss tangent will disappear if adding montmorillonite into the composite. It was also found that the T_g of the exfoliated nanocomposite decreases with increasing montmorillonite loading. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 842–849, 2002; DOI 10.1002/app.10354