Study on the effect of woven sisal fiber mat on mechanical and viscoelastic properties of petroleum based epoxy and bioresin modified toughened epoxy network

Sisal fiber reinforced biocomposites are developed using both unmodified petrol based epoxy and bioresin modified epoxy as base matrix. Two bioresins, epoxidized soybean oil and epoxy methyl soyate (EMS) are used to modify the epoxy matrix for effective toughening and subsequently two layers of sisal fiber mat are incorporated to improve the mechanical and thermomechanical properties. Higher strength and modulus of the EMS modified epoxy composites reveals good interfacial bonding of matrix with the fibers. Fracture toughness parameters K_IC and G_IC are determined and found to be enhanced significantly. Notched impact strength is found to be higher for unmodified epoxy composite, whereas elongation at break is found to be much higher for modified epoxy blend. Dynamic mechanical analysis shows an improvement in the storage modulus for bioresin toughened composites on the account stiffness imparted by fibers. Loss modulus is found to be higher for EMS modified epoxy composite because of strong fiber–matrix interfacial bonding. Loss tangent curves show a strong influence of bioresin on damping behavior of epoxy composite. Strong fiber–matrix interface is found in modified epoxy composite by scanning electron microscopic analysis. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42699.     

Influence of complexing treatment and epoxy resin coating on the properties of aramid fiber reinforced natural rubber

In this work, natural rubber/aramid fiber (NR/AF) composites were prepared with master batch method. AF was modified by using epoxy resin (EP) and accelerator 2‐ethyl‐4‐methylimidazole (2E4MZ) through surface coating on the basis of the complexing treatment with CaCl₂ solution. Hydroxyl‐terminated liquid isoprene rubber (LIR) was regarded as a compatibilizer between EP and NR. It is found that the crystallinity on AF surface is decreased by complexing reaction with CaCl₂ solution. Swelling and mechanical properties of the vulcanized composites, such as swelling degree, tensile and tear strength, tensile modulus at 300% elongation, are measured, and the tensile fracture morphology and dynamic mechanical analysis of the composites are investigated. The results show that the mechanical properties of composites with modified fibers are improved obviously and interfacial adhesion between matrix and the fiber is enhanced, especially for the AF coated with EP and imidazole. The best comprehensive mechanical properties of the composites are obtained with using CaCl₂‐EP/2E4MZ system when the ratio of m(EP)/m(AF) is 3%. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42122.     

Effect of multi‐walled carbon nanotubes dispersity on the light transmittancy of multi‐walled carbon nanotubes/epoxy composites

Two types of multi‐walled carbon nanotubes (MWCNTs), chemically modified and unmodified, were dispersed in epoxy resin with ultrasonication. The light transmittance characteristics of epoxy composites with different ratios of MWCNTs to epoxy resin were measured at wavelengths ranging from 200 to 1100 nm. Results showed that composites with modified MWCNTs had a much higher light transmittance than those with unmodified MWCNTs. This was presumably due to a more uniform dispersion of modified MWCNTs in the epoxy matrix, as indicated by both transmission electron microscopy and optic microscopy. The wavelength dependency of light transmittance of the composites was expressed empirically as a function of weight fraction (f_w) of MWCNTs and the light wavelength (λ). POLYM. ENG. SCI. 46:635–642, 2006. © 2006 Society of Plastics Engineers.     

Effects of high nano‐SiO2 contents on properties of epoxy‐modified polybenzoxazine

High‐performance nanosilica composites based on epoxy‐modified polybenzoxazine matrices are developed. Chemorheological study of benzoxazine–epoxy resin mixtures reveals that processing window of the benzoxazine resin (BA‐a) is substantially broadened with an addition of the liquid epoxy. Glass transition temperature (T _g) of the BA‐a copolymerized with epoxy resin shows a synergistic behavior with a maximum T _g value (174°C) at the benzoxazine–epoxy mass ratio of 80:20. The copolymer at this composition is also used as a matrix for nano‐SiO₂ composites. A very low melt viscosity of the benzoxazine–epoxy mixtures promotes good processability with the maximum attainable nano‐SiO₂ loading up to 35 wt%. From scanning electron microscopy investigation, fracture surface of the 35 wt% nano‐SiO₂‐filled benzoxazine–epoxy composite reveals relatively homogeneous distribution of the nano‐SiO₂ in the copolymer with good particle wet‐out. In addition, very high reinforcing effect was also observed in such high content of the nano‐SiO₂, i.e., about 2.5 times in modulus improvement. This improvement is attributed to the strong bonding between the copolymer matrix and the nano‐SiO₂ through ether linkage as confirmed by Fourier‐transform infrared investigation. POLYM. COMPOS., 38:2261–2271, 2017. © 2015 Society of Plastics Engineers     

Transparent dispensible high‐refractive index ZrO2/epoxy nanocomposites for LED encapsulation

In this study, we report a facile ex situ approach to preparing transparent dispensible high‐refractive index ZrO₂/epoxy nanocomposites for LED encapsulation. Highly crystalline, near monodisperse ZrO₂ nanoparticles (NPs) were synthesized by a nonaqueous approach using benzyl alcohol as the coordinating solvent. The synthesized particles were then modified by (3‐glycidyloxypropyl)trimethoxysilane (GMS) ligand. It was found that, with tiny amount of surface‐treating ligand, the modified ZrO₂ NPs were able to be easily dispersed in a commercial epoxy matrix because of the epoxy compatible surface chemistry design as well as the small matrix molecular weight favoring mixing. Transparent thick (1 mm) ZrO₂/epoxy nanocomposites with a particle core content as high as 50 wt % and an optical transparency of 90% in the visible light range were successfully prepared. The refractive index of the prepared composites increased from 1.51 for neat epoxy to 1.65 for 50 wt % (20 vol %) ZrO₂ loading and maintained the same high‐Abbe number as the neat epoxy matrix. Compared with the neat epoxy encapsulant, an increase of 13.2% in light output power of red LEDs was achieved with the 50 wt % ZrO₂/epoxy nanocomposite as the novel encapsulant material. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3785–3793, 2013     

Effect of Al2O3 addition on thermo‐electrical properties of polymer composites: An experimental investigation

To develop a new class of composites with adequately high thermal conductivity and suitably controlled dielectric constant for electronic packages and printed circuit board applications, polymer composites are prepared with microsized Al₂O₃ particle as filler having an average particle size of 80–100 μm. Epoxy and polypropylene (PP) are chosen as matrix materials for this study. Fabrication of epoxy‐based composite is done by hand lay‐up technique and its counterpart PP‐based composite are fabricated by compression molding technique with filler content ranging from 2.5–25 vol%. Effects of filler loading on various thermal properties like effective thermal conductivity (k_eff), glass transition temperature (T_g), coefficient of thermal expansion (CTE) and electrical property like dielectric constant (ε_c) of composites are investigated experimentally. In addition, physical properties like density and void fraction of the composites along with there morphological features are also studied. The experimental findings obtained under controlled laboratory conditions are interpreted using appropriate theoretical models. Results show that with addition of 25 vol% of Al₂O₃, k_eff of epoxy and PP improve by 482% and 498% respectively, T_g of epoxy increases from 98°C to 116°C and that of PP increases from −14.9°C to 3.4°C. For maximum filler loading of 25 vol% the CTE decreases by 14.8% and 26.4% for epoxy and PP respectively whereas the dielectric constants of the composites get suitably controlled simultaneously. POLYM. COMPOS., 36:102–112, 2015. © 2014 Society of Plastics Engineers     

Thermal stability and kinetics analysis of epoxy composites modified with reactive polyol diluent and multiwalled carbon nanotubes

The effect of polyether polyol and amino‐functionalized multiwalled carbon nanotubes (NH₂‐MWCNTs) on the thermal stability of three‐phase (epoxy/polyol/NH₂‐MWCNTs) epoxy composites was investigated. Thermal stability and degradation characteristics of polyol/MWCNTs modified epoxy composites was evaluated using thermogravimetric analysis. The kinetics of thermal degradation was assessed from data scanned at 5, 10, and 20°C/min. Activation energy for degradation of epoxy nanocomposites was calculated using different differential and integral methods, that is, Kissinger's, Flynn–Wall–Ozawa, Coats–Redfern, and Horowitz–Metzger methods. In addition, the integral procedure decomposition temperature was determined to evaluate the inherent thermal stability of the modified composite system. Rate of thermal degradation in MWCNT/Polyol samples was found to be reduced significantly while activation energy of degradation was increased compared to unmodified epoxy composite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41558.     

High performance polyamide 6 composites prepared by reactive extrusion

To improve the properties of polyamide 6 (PA6) composites, a series of modified PA6 composites was prepared by reaction extrusion. An amorphous PA6 was first obtained by the complexing reaction of Li⁺ in lithium chloride with amino groups, and then epoxy resins, nano‐SiO₂ as well as POE‐g‐MAH were in turn added into the PA6/LiCl system. The effect of different additives on the crystallization behavior and mechanical properties of PA6 composites was well‐studied by X‐ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), and mechanical properties tests. The results demonstrated that PA6 was amorphous at 6 phr lithium chloride and a network structure was formed in PA6 matrix in the presence of epoxy resins, thus the mechanical properties of composites greatly were enhanced. However too many nano‐SiO₂ particles might impair the tensile strength of PA6 composites. Additionally, a PA6 composite with excellent properties was obtained in the presence of POE‐g‐MAH due to the crystal form change in PA6 matrix and the strong interaction between PA6 and POE‐g‐MAH. POLYM. COMPOS., 35:985–992, 2014. © 2013 Society of Plastics Engineers     

Synthesis of carbon quantum dots/TiO2 nanocomposite for photo-degradation of Rhodamine B and cefradine

Pure TiO₂ and carbon quantum dots (CQDs)-doped TiO₂ nanocomposite (CQDs/TiO₂ nanocomposite) were prepared by a sol-gel approach for photocatalytic removal of Rhodamine B and cefradine. Analyses by Transmission electronmicroscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), UV–visible spectroscopy and X-ray powder diffraction (XRD) confirmed the successful formation of CQDs/TiO₂ heterostructure. The as-prepared TiO₂ and CQDs/TiO₂ composite possessed small particles, spherical-like shape, and anatase crystal form. Meanwhile, Rhodamine B and cefradine were chosen to evaluate the photocatalytic activity of TiO₂ and CQDs/TiO₂ composite. Results revealed that with the facile decoration of CQDs, the absorption of photocatalyst was extended into visible light region and photocatalytic activity was improved in comparison with pure TiO₂. Furthermore, the mechanism for the improvement of the photocatalytic performance of the composites was discussed on the basis of the results. CQDs play an important role in the photocatalytic process, due to their superior ability to extend the visible absorption and produce more electrons and electron–hole pairs for the degradation of pollutants. In all, the paper offers further insights into the development of CQDs/TiO₂ nanocomposite as photocatalyst for the degradation of antibiotics.     

Mechanical properties and fracture behaviors of epoxy composites with phase‐separation formed liquid rubber and preformed powdered rubber nanoparticles: A comparative study

Epoxy composites filled with phase‐separation formed submicron liquid rubber (LR) and preformed nanoscale powdered rubber (PR) particles were prepared at different filler loading levels. The effect of filler loading and type on the rheological properties of liquid epoxy resin suspensions and the thermal and mechanical properties of the cured composites as well as the relative fracture behaviors are systematically investigated. Almost unchanged tensile yield strength of the cured epoxy/PR composites is observed in the tensile test compared with that of the neat epoxy; while the strength of the cured epoxy/LR composites shows a maximum value at ∼4.5 wt% and significantly decreases with increasing LR content. The glass transition temperature (T_g) of the cured PR/epoxy has shifted to the higher temperature in the dynamic mechanical thermal analysis compared with that of the cured pure epoxy and epoxy/LR composites. Furthermore, the presence of LR results in highly improved critical stress intensity factor (K_IC) of epoxy resin compared with the corresponding PR nanoparticles. In particular, the PR and LR particles at 9.2 wt% loading produce about 69 and 118% improvement in K_IC of the epoxy composites, respectively. The fracture surface and damage zone analysis demonstrate that these two types of rubber particles induce different degrees of local plastic deformation of matrix initiated by their debonding/cavitation, which was also quantified and correlated with the fracture toughness of the two epoxy/rubber systems. POLYM. COMPOS., 36:785–799, 2015. © 2014 Society of Plastics Engineers     

In situ synthesis and enhanced visible light photocatalytic activity of C-TiO2 microspheres/carbon quantum dots

TiO₂ microspheres and TiO₂/carbon quantum dots (CQDs) composites with different CQDs contents were successfully synthesized via solvothermal and in situ hydrothermal method. The structure and morphology of the prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). Results showed that carbon elements were successfully doped into the TiO₂ lattice (C-TiO₂) and CQDs were hybrid with C-TiO₂ microspheres. The X-ray photoelectron spectroscope (XPS), valence band XPS (VB-XPS) and UV–vis diffuse reflectance spectra (DRS) analyses revealed that carbon doped into TiO₂ microspheres could lead to local energy levels in the band structure and generate valence band tails to absorb visible light. The photocatalytic activities of these samples were evaluated by the photodegradation of Rhodamine B (RhB) under visible light irradiation. C-TiO₂/CQDs samples presented an enhanced photocatalytic performance compared with pristine TiO₂, which could be attributed to the present of CQDs, acting as adsorption sites for RhB molecules and charge separation centers to impede the recombination and prolong the life time of electron and hole pairs.     

Mechanical and thermal properties of biphenyldiol formaldehyde resin/gallic acid epoxy composites enhanced by graphene oxide

In this study, the gallic acid‐based epoxy resin (GA‐ER) and alkali‐catalysed biphenyl‐4,4′‐diol formaldehyde resin (BPFR) are synthesized. Glass fibre‐reinforced GA‐ER/BPFR composites are prepared. Graphene oxide (GO) is used to improve the mechanical and thermal properties of GA‐ER/BPFR composites. Dynamic mechanical properties and thermal, mechanical, and electrical properties of the composites with different GO content are characterized. The results demonstrate that GO can enhance the mechanical and thermal properties of the composites. The glass transition temperature, T_g, of the BPFR/GA‐ER/GO composites is 20.7°C higher than the pure resin system, and the 5% weight loss temperature, T_d5, is enhanced approximately 56.6°C. When the BPFR: GA‐ER mass ratio is at 4 : 6 and GO content is 1.0–1.2 wt %, the tensile and impact strengths of composites are 60.97 MPa and 32.08 kJ/m² higher than the pure resin composites, respectively. BPFR/GA‐ER composites have better mechanical properties, and can replace common BPA epoxy resins in the fabrication of composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42637.     

Enhancing the thermal conductivities of SiO2/Epoxy composites by orientation

To improve the thermal conductivity of epoxy resin, tensile way was used to orient the molecular chain of epoxy resin with SiO₂ particles filled. In this article, SiO₂/Epoxy composites which had approximately one‐dimensional lattice structure were prepared. The heat generated by LED chip rapidly passed along the direction of the one‐dimensional orientation in SiO₂/Epoxy composites. The results showed that the thermal conductivity of oriented composites increased with the increase of silica concentration and draw ratio (If S is the cross‐sectional areas of composites at the mold outlet, S₀ is the cross‐sectional areas of composites after molding set, and draw ratio is S/S₀). With the addition of 50 wt% SiO₂ to the epoxy resin, the thermal conductivity of oriented SiO₂/Epoxy composites with the draw ratio of 4 was 0.873 W/m K, which was 2.55 times that of unoriented SiO₂/Epoxy composites. And a thermal conductivity, 5.97 times that of the epoxy resin, was obtained with 80 wt% SiO₂ and the draw ratio of 4. Nevertheless, the relative permittivities of epoxy composites which had 50 wt% SiO₂ with the draw ratio of 4 are stable with increasing frequency. POLYM. COMPOS., 37:818–823, 2016. © 2014 Society of Plastics Engineers     

In situ thermal reduction of graphene oxide forming epoxy nanocomposites and their dielectric properties

The electrical properties of epoxy based composites modified by low amounts of graphite oxide, below the conduction threshold, have been investigated. The composites have been prepared without the use of solvents by direct sonication of graphite oxide (GO) powders and of chemically modified and partially reduced GO powders in the based epoxy monomer. Through a mild thermal treatment, in situ reduction of the previously dispersed GO has been obtained directly inside the epoxy resins. The changes in the electrical response of the materials thus obtained have been compared to that of pristine unmodified epoxy resin. Data so far collected underline the possibility to tune the electrical conductivity of the composites within two orders of magnitude and to increase the values of permittivity without significantly worsening dielectric losses. POLYM. COMPOS., 36:294–301, 2015. © 2014 Society of Plastics Engineers     

Mechanical behavior and fracture toughness of epoxy composites reinforced with combination of fibrous and spherical nanofillers

Epoxy nanocomposites modified with multiwalled carbon nanotubes (MWNTs), rubber nanoparticles (RNPs), and the combinations of MWNTs and RNPs were prepared. The effects of multiphase reinforcements on mechanical and fracture properties of epoxy resin were investigated. With combined use of RNPs and MWNTs, the ternary nanocomposites exhibit simultaneous enhancement in stiffness, strength and fracture toughness. Maximum increase of 101% in K_IC and 294% in G_IC of the ternary composites were achieved in this study. A modified model was developed to predict the modulus of the ternary composites based on the Halpin‐Tsai equation, which was proved to match the experimental results exactly. DSC, TEM, SEM, and AFM studies were carried out to evaluate the composition and microstructure of the binary and ternary composites. POLYM. COMPOS., 36:2147–2156, 2015. © 2014 Society of Plastics Engineers     

Epoxy composites reinforced by different size silica nanoparticles

Three series of epoxy/SiO₂ composites, containing 0.3–7 wt % nanosized SiO₂ with different specific surface area, were prepared by solution blending. The resulting composites exhibit the higher glass transition temperature (T_g) than that of pure epoxy. The T_g of composite showed a maximum increment of 35.3°C by the addition of 7 wt % A300. The trade name of A300 is Aerosil 300. It is one of the fumed silica nanoparticles products of Degussa. The decomposition temperatures (T_d) of composites were always higher than that of pure epoxy and showed a maximum increment of 20.8°C by the addition of 5 wt % A300. The light transmittance of composites was as a function of the SiO₂ content and size. The water permeability of composites decreased with increasing SiO₂ content and the 7 wt % A300 composite exhibits a maximum decrement percentage of 35.6%. The T_g, T_d, storage modulus, and water‐vapor barrier property are as a function of the SiO₂ content and size. These properties increased as the content of SiO₂ increased. The finer SiO₂ are more effective in increasing the T_g, T_d, and water‐vapor barrier property. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Nano‐SiO2/PMMA‐PU composite particles with core‐shell structure via emulsion polymerization and their application in epoxy resin

A novel method of nano‐SiO₂/poly(methyl methacrylate)(PMMA)‐polyurethane(PU) composite particles modifying epoxy resin is reported. The composite particles with the obvious core‐shell structure were prepared by emulsion polymerization of PMMA and PU prepolymer on the surface of nano‐SiO₂. The diameter of the composite particles was 50–100 nm with dark core SiO₂ (30–60 nm) and light shell polymer of PMMA and PU (20–30 nm); moreover, PU was well distributed in PMMA with about 10 nm diameter. After nano‐SiO₂ was encapsulated by PMMA and PU, the Si content on the surface decreased rapidly to 2.08% and the N content introduced by PU was about 1.27%. The ratio of polymer to original nano‐SiO₂ (f_p), the grafting ratio of polymer to original nano‐SiO₂ (f_r) and the efficiency grafting ratio of polymer (f_e) were, respectively, about 116.7%, 104.4%, and 89.5%. The as‐prepared composite particles were an effective toughness agent to modify epoxy resin, and the impact strength of the modified epoxy resin increased to 46.64 kJ m^?2 from 19.12 kJ m^?2 of the neat epoxy resin. This research may enrich the field of inorganic nanoparticles with important advances toward the modification for polymer composite materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41919.     

Influences of different gravity environments on the curing process and cured products of carbon‐nanotube‐reinforced epoxy composites

The influences of different gravity environments on the curing process and the cured products of carbon‐nanotube‐reinforced epoxy composites were investigated in this study. Different gravity environments were simulated with a superconducting magnet on the basis of which resin matrix composites with different amino‐functionalized multiwalled carbon nanotube (NH₂‐MWCNT) concentrations of 0.1, 0.3, 0.5, and 1 wt % were tested. Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, thermomechanical analysis (TMA), thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and three‐point bending tests were used to analyze the characteristics of different curing processes and cured products. From the results, we observed that the curing rate of the epoxy composites was influenced by different gravity values, and there was anisotropy in the NH₂‐MWCNT‐reinforced epoxy composites cured in the simulated microgravity environment. More effects of gravity on the curing process and cured products could be obtained through detailed experiments and discussion; this is important and fundamental for improving and enhancing the properties of composite materials used in different gravity environments. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41413.     

Resin modification on interlaminar shear property of carbon fiber/epoxy/nano‐CaCO3 hybrid composites

Epoxy resin was modified by adding a silane coupling agent/nano‐calcium carbonate master batch. Then, samples of binary carbon fiber/epoxy composites and ternary fiber/nano‐CaCO₃/epoxy were prepared by hot press process. The interlaminar shear strength (ILSS) of the carbon fiber/epoxy composites was investigated and the results indicate that introduction of the treated nano‐CaCO₃ enhances ILSS obviously. In particular, the addition of 4 wt% nano‐CaCO₃ leads to 36.6% increase in the ILSS for the composite. The fracture surfaces of the carbon fiber/epoxy composites and the mechanical properties of epoxy resin cast are examined and both of them are employed to explain the change of ILSS. The results show that the change of ILSS is primarily due to an increase of the epoxy matrix strength and an increase of the fiber/epoxy interface. The bifurcation of propagating cracks, stress transfer, and cavitation are deduced for the reasons of strengthening and toughening effect of nano‐CaCO₃ particles. POLYM. COMPOS., 38:2035–2042, 2017. © 2015 Society of Plastics Engineers     

Investigations on the surface structure and properties of silica‐polyamine composites on the nanoscales and microscales

The structure and properties of silica polyamine composites (SPC) made from microparticles of amorphous silica gel (300–600 microns) and silica nanoparticles (10–20 nm) modified with aminopropyltrimethoxysilane (APTMS), poly(allylamine) (PAA) or poly(ethyleneimine) (PEI) have been studied. The APTMS nano‐hybrids showed batch capacities for copper equal to or better than the corresponding polymer‐based micro‐hybrids. Loading of the PEI on the nanoparticles was independent of molecular weight of the polymer. Dynamic light scattering measurements showed that the SiO₂ nanoparticles and the composites made from them aggregate in water and the degree of aggregation is dependent on the surface modification. All of the amine‐modified materials were catalysts for the Knoevenagel reaction but interestingly, the microparticles modified with APTMS were better catalysts than the corresponding nanoparticles or the polyamine modified composites. Solid‐state ¹⁹Si NMR has been used to elucidate the surface structure of the various composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42271.