UV-waterborne polyurethane-acrylate nanocomposite coatings containing alumina and silica nanoparticles for wood: mechanical, optical, and thermal properties assessment

The effect of alumina and silica nanoparticles on mechanical, optical, and thermal properties of UV-waterborne nanocomposite coatings was investigated. The addition of nanoalumina and nanosilica was shown to decrease the hardness because of nanoparticle aggregation. In comparison to the neat coating and despite the presence of aggregates, the scratch resistance of nanocomposite coatings was significantly improved. As expected, the gloss of UV-waterborne coatings was reduced following the addition of nanoparticles due to an increase of the surface roughness. Alumina and silica nanoparticles were found to enhance the glass transition temperature of PUA nanocomposite coatings by hindering the mobility of macromolecular chains at the interface around the nanoparticles. Finally, the interest and efficiency of grafting trialkoxysilanes was demonstrated with the study of nanosilica behavior. Not only was the dispersion of nanosilica enhanced following trialkoxysilanes grafting onto silica nanoparticles, but also the scratch resistance and the adhesion of UV-waterborne coatings containing nanosilica markedly increased even with 1 wt% content. Silica which is recommended in the wooden furniture and kitchen cabinet manufacturing industry as nano-reinforcement provides improved properties well suited in surface coating applications to efficiently protect surface of wood substrates.     

Effect of organosilane coupling agents on microstructure and properties of nanosilica/epoxy composites

Three types of silane coupling agents, γ‐aminopropyltriethoxysilane, γ‐glycidoxypropyltrimethoxysilane, and γ‐methacryloxypropyltrimethoxysilane, were used as modifiers to modify the surface of the nanosilica, respectively, and the nanocomposites of the epoxy resin filled with nano‐sized silica modified by three silane coupling agents were prepared by physical blending. The properties of the modified silica nanoparticles were characterized by Fourier transform infrared spectrum and particle‐size analyzer. The microstructure, mechanical behavior, and heat resistant properties of the nanocomposites were investigated by transmission electron microscopy, scanning electron microscopy, thermo gravimetric analyses, differential thermal gravity, differential scanning calorimetry, and flexural tests. The results showed that these modifiers are combined to the surfaces of nanosilica by the covalent bonds, and they change the surface properties of nanosilica. The different structures of coupling agents have different effects on the dispersibility and stability of modified particles in the epoxy matrix. In comparison, the silica nanoparticles modified by γ‐glycidoxypropyltrimethoxysilane exhibit a good dispersivity. The nanocomposites with 4 wt% weight fraction nanosilica modified by γ‐glycidoxypropyltrimethoxysilane have higher thermal decomposing temperature and glass transition temperature than those of the other two composites with the same nanosilica contents, and they are raised by 43.8 and 8°C relative to the unmodified composites, respectively. The modified silica nanoparticles have good reinforcing and toughening effect on the epoxy matrix. The ultimate flexural strengths of the composites with 4 wt% nanoparticles modified by γ‐aminopropyltriethoxysilane, γ‐glycidoxypropyltrimethoxysilane, and γ‐methacryloxypropyltrimethoxysilane are increased by 10, 30, and 8% relative to the unmodified composites, respectively. The flexural fracture surfaces of modified composites present ductile fracture features. POLYM. COMPOS. 2012. © 2012 Society of Plastics Engineers     

Preparation and characterization of thermoplastic olefin/nanosilica composites using a silane-grafted polypropylene matrix

This work reports the morphology and physical properties of silane-grafted polypropylene (PP-g-VTEOS) reinforced with silica nanoparticles and toughened with an elastomeric ethylene-octene copolymer (POE). Vinyltriethoxysilane (VTEOS) was grafted to polypropylene (PP) to form (PP-g-VTEOS), using a peroxide-initiated melt compounding technique. TEM observations of composites containing up to 7 wt% of the nanosilica revealed good dispersion of the silica nanoparticles, which partitioned selectively within the PP-g-VTEOS matrix. Rheological characterization in the linear viscoelasticity region showed significant increases in the low-frequency complex viscosity, storage and loss moduli, which stem from the polymer/filler and filler/filler interactions. The effects of surface treatment of the nanosilica on the morphology, thermal and mechanical properties of the composites were also investigated. The mechanical properties of the composites were greatly enhanced in terms of tensile and flexural strength, while impact strength was preserved when the silane-treated nanosilica was used.     

Transparent cyclic olefin copolymer/silica nanocomposites

In this work, melt blending of fumed nanosilica with cyclic olefin copolymer (COC) was carried out to prepare high strength transparent composites. The effects of various loadings (1, 2, 3 and 5 wt%) of nanosilica on the physical, mechanical, dynamic mechanical, thermal, tribological and optical properties of the COC composites were investigated in detail. The tensile test results showed that the nanocomposite with 3 wt% nanosilica content provides the highest tensile strength (55.6 MPa) compared with the nanocomposite with 5 wt% nanosilica content (54.6 MPa), which is believed to be significantly dependent on better dispersion. Moreover, the glass transition temperature (from tan δ) increased from 184 °C for pure COC to 194.3 °C for the COC composite with 3 wt% nanosilica. The scratch test and nano‐indentation results showed that addition of nanosilica increased the stiffness and hardness of the composite, providing higher scratch resistance and lower frictional coefficient. UV?visible spectroscopy measurements showed that the nanocomposites have excellent optical transparency which is similar to that of the pure COC film. © 2013 Society of Chemical Industry     

Solvent-Free One-Pot Synthesis of high performance silica/epoxy nanocomposites

High performance silanized silica/epoxy nanocomposites were prepared through mixing epoxy, tetraethyl orthosilicate (TEOS), (3-aminopropyl)trimethoxysilane (APTMS) and ammonia solution at 50 °C. This all-in-one “Solvent-Free One-Pot Synthesis” results in nanocomposites with uniform dispersion of oval shaped silica nanoparticles and strong adhesion between silica and epoxy matrix. The influence of the synthesis conditions, such as molar ratio of NH₃:TEOS, aging time, curing process and silica content on the thermal mechanical properties of nanocomposites were studied. The silanized silica/epoxy nanocomposite prepared in this study exhibits better thermal mechanical property in comparison with neat epoxy, non-functionalized silica/epoxy and commercialized silica/epoxy systems. The prepared nanocomposite with 3 wt% silanized silica exhibits 20%, 17% and 6% improvements on flexural, tensile and storage modulus over those of neat epoxy, respectively.     

Investigation on Sound Absorption Function and Mechanical Behavior of Polycarbonate/Nanosilica-based Nanocomposites

The present study reports the morphological, mechanical, and sound absorption properties of polycarbonate-based nanocomposites containing nanosilica (0.3 and 0.6?wt%). To this end, the specimens were prepared by melt mixing in a twin-screw extruder. The scanning electron microscopy was also used to ensure the well distribution of nanosilica in the polymeric matrix. The mechanical properties were investigated by tensile, flexural strength, Izod impact, and hardness tests. At the end, sound absorption coefficient of the specimens was checked by standing wave sound impedance tube method in the frequency range of 250–6,300?Hz. The results showed that only a small amount of nanosilica could improve the mechanical properties of specimens. However, the sound absorption function of specimens had a gradual improvement by increasing nanosilica content. Tensile modulus and strength at yield of the nanocomposite specimens were higher than that of the neat polycarbonate. On the contrary, a decrease in elongation at break was reported, which was attributed to the reduced mobility of the polymer chains due to the presence of nanoparticles. The same behavior was observed in the test results of Izod impact strength of nanocomposites so that adding nanosilica with the wt% of 0.6 to the neat polycarbonate, the impact strength improved by only 5.3%. According to the findings, polycarbonate composites with 0.3?wt% nano-silica, in addition to strengthening the mechanical properties (tensile modulus, flexural strength, and stiffness), could improve the acoustic characteristics of the specimens in low and mid frequencies. The findings also revealed that the performance of pure polycarbonate and 6?wt% nanosilica polycarbonate in upper frequency range was higher and approximately the same as that for 3?wt% nanosilica polycarbonate.     

Polymer nanocomposites for bone tissue substitutes

Following the quest for new composite biomaterials for bone tissue engineering, this work presents the processing of new nanocomposite made of polycaprolactone matrix and wollastonite particles. Wollastonite nanopowder was obtained by thermal treatment of polymethyloxosilane resin mixed with silica and calcium hydroxide. Bioactive character of the ceramic nanopowder was verified in simulated body fluid (SBF). The apatite formation on wollastonite grain surface after immersion in SBF was observed. Basic mechanical properties of the samples containing various amount of ceramic nanoparticles have been examined. It was shown that the presence of small amount of wollastonite nanoparticles (0.5–1.0 wt%) improves significantly the Young's modulus, tensile strength, and work-of-fracture of polymer matrix composite. Increased content of ceramic nanoadditive (>2%) in nanocomposites resulted in degradation of their mechanical characteristics.     

Influence of dual-component microcapsules on self-healing efficiency and performance of metal-epoxy composite-lap joints

Dual-component microcapsules were synthesized by solvent evaporation technique using epoxy resin and hardener as core materials and polymethyl methacrylate (PMMA) as shell wall materials. Morphology, core content, and size distribution of microcapsules were monitored by controlling the various processing parameters such as agitation speed, core–shell weight ratio, and concentration of emulsifiers. The molecular structure, morphologies, and thermal characteristics of the microcapsules were examined under Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and thermogravimetric analysis (TGA), respectively. Synthesized dual-component microcapsules were entrenched into the epoxy polymer to introduce the healing features in single lap shear epoxy adhesive joints. Healing efficiency as high as 89% was achieved when 10 wt% dual-component microcapsules were introduced in adhesives. Investigation of the fractured surfaces of the healing enabled adhesives reveals the presence of crack pinning and crack blunting sites represented by characteristic tails at the wake of microcapsules in cohesive zone. Such failure mechanisms responsibly influence the healing efficiency.     

Effect of inorganic nanoparticles on mechanical property, fracture toughness and toughening mechanism of two epoxy systems

We investigated the effect of silica nanoparticles on the mechanical property and fracture toughness of two epoxy systems cured by Jeffamine D230 (denoted J230) and 4,4′-diaminodiphenyl sulfone (denoted DDS), respectively. Toughening mechanisms were identified by a tailor-loaded compact tension method which quantitatively recorded the deformation of a damage zone in the vicinity of a sub-critically propagated sharp crack tip. 20 wt% silica nanoparticles' fraction provided 40% improvement in Young's modulus for both systems; it improved the toughness of J230-cured epoxy from 0.73 to 1.68 MPa m^1/2, and for the other system improved from 0.51 to 0.82 MPa m^1/2. The nanoparticles not only stiffen, strengthen and toughen epoxy, but reduce the effect of flaws on mechanical performance as well. In both systems, nanosilica particle deformation, internal cavitation and interface debonding were not found, different to previous reports. This could be due to the various hardeners used or different identification techniques employed. The toughening mechanisms of the J230-cured nanocomposite were attributed to the formation and development of a thin dilatation zone and nanovoids, both of which were induced, constrained and thwarted by the stress fields of the silica nanoparticles. Regarding 10 wt% silica-toughen epoxy cured by J230, a thicker and shorter dilatation zone was found, where neither nanoparticles nor nanovoids were observed. With regard to the DDS-cured system, much less dilatation and voids were found due to the hardener used, leading to moderately improved toughness.     

Effect of silica nanoparticles on structure and properties of waterborne UV-curable polyurethane nanocomposites

UV-curable waterborne polyurethane (WUPU)/silica nanocomposites were prepared using various silica by phase-inversion emulsification method. TEM examinations of nanostructured films indicated that the organic modified nanosilica was well dispersed in the WUPU matrix, while the acid and alkaline silica formed much less compact, or densely aggregated structure. DMA analysis demonstrated that the WUPU/silica nanocomposite films had a broadening of the tanδ peak and shifted to higher temperature. The WUPU/silica nanocomposite films displayed enhanced storage modulus, Shore A hardness, tensile strength without sacrificing high elongation at break compared to that of the pure WUPU film. The resulting nanocomposite films are possibly interesting for the generation of waterborne UV-curable transparent coatings with scratch-resistance.     

Mechanical properties of hybrid structural composites reinforced with nanosilica

Epoxy‐based hybrid structural composites reinforced with 14 nm spherical silica particles were investigated for mechanical properties as a function of nanosilica loading fractions. Composites were fabricated using continuous glass or carbon fiber of unidirectional architecture and nanosilica dispersed epoxy, through resin film infusion process. Uniform dispersion of nanoparticles in resin matrix was ensured by an optimized ultrasound‐assisted process. Although resin viscosity marginally reduces in the presence of nanosilica enabling a better control in composite manufacturing process, glass transition temperature of epoxy remained unaffected at low weight fractions. Compressive strength of hybrid glass or carbon fiber/epoxy composites showed more than 30–35% increase with nanosilica at a concentration as low as 0.2 wt%. Tensile and compressive properties of hybrid composites in transverse direction to the reinforcement remained unaffected. POLYM. COMPOS. 37:1216–1222, 2016. © 2014 Society of Plastics Engineers     

Improvement in mechanical and thermal properties of unsaturated polyester- based hybrid composites

Polymer matrix composites are used in automobile, structure and aerospace industries due to their light weight and high strength. The present research has an aim to reinforce locally developed silica nanoparticles and glass fibers in unsaturated polyester to produce polymer-based hybrid composites. Composites were synthesized by hand lay-up method with 1, 2, 3 and 4 wt% of silica sand nanoparticles and glass fiber. Mechanical tests like tensile, impact and micro-hardness were performed on the obtained polymer hybrid composites. The results of mechanical properties of the hybrid polymer matrix composites revealed an increasing trend. The SEM analysis was performed on the developed and fractured tensile testing samples. The SEM analysis showed the presence of silica nanoparticles in the samples and pulling action of fibers were seen under fractured tensile tests. The pulling actions of fibers from polymer matrix delayed the fractured mechanism and enhanced the mechanical properties. Silica nanoparticles filled the cavities generated during tensile test and extensive enhancement was revealed in tensile as well as impact energy. Toughness of the hybrid composite was also enhanced as a result. The thermal properties of the hybrid polymer composites were analyzed using thermogravimetric analysis. Thermal stability of the composite has been marginally increased with increasing wt% of reinforcement.     

Characterization and properties of activated nanosilica/polypropylene composites with coupling agents

In this work, nanosilica/polypropylene composites containing 1 wt% of silica nanoparticles were prepared by melt mixing in a Thermo Haake internal mixer. Prior compounding, nanosilica was subjected to surface activation using sodium hydroxide (NaOH) solution. The effectiveness of the activation process was evaluated by measuring the amount of hydroxyl groups ( OH) on the surface of nanosilica via titration method and supported by FTIR analysis. Two coupling agents namely 3‐aminopropyl triethoxysilane (APTES) and neopentyl (diallyl)oxy, tri(dioctyl) phosphate titanate (Lica 12) were used for surface treatment after activation process. The mechanical properties of polypropylene matrix reinforced with silica nanoparticles were determined by tensile and impact test. Hydroxyl groups on the nanosilica surface played an important role in enhancing the treatment with silane coupling agents. To increase the amount of hydroxyl groups on the nanosilica surface, the optimum concentration of NaOH is 1 mol%. Tensile strength, tensile modulus, and impact strength of nanosilica/PP composites improved with activation process. As the coupling agent is concerned, APTES coupling agent is more pronounced in enhancing the mechanical properties of the composites when compared with Lica 12 coupling agent. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Friction spot welding of PMMA with PMMA/silica and PMMA/silica-g-PMMA nanocomposites functionalized via ATRP

In the present study, the feasibility of Friction Spot Welding (FSpW) of a commercial-grade poly(methyl methacrylate) (PMMA) (PMMA GS) and PMMA 6N/functionalized silica (SiO₂) nanocomposites was investigated. The silica nanoparticles were functionalized via atom transfer radical polymerization (ATRP) with PMMA chains to achieve a uniform dispersion in the polymer matrix. The successful functionalization of silica nanoparticles with PMMA chains via ATRP was evaluated by ATR-FT-IR and TGA measurements. Rheological investigations of the silica nanocomposites showed a plateau of the storage modulus G′ at low frequencies (0.01–0.03 rad/s) as a result of elastic particle–particle interactions. Overlap friction spot welds consisting of PMMA GS and a 2 wt% SiO₂-g-PMMA nanocomposite were successfully prepared and compared to spot joints of PMMA GS welded with PMMA 6N and PMMA 6N/silica nanocomposite with 2 wt% unfunctionalized silica nanoparticles. Raman mappings of selected areas of cross-sectional plastographic specimens revealed an increased mixing behavior between the two polymer plates in the case of PMMA GS/2 wt% SiO₂-g-PMMA joints. Although the joints welded with PMMA 6N/silica nanocomposites showed a reduction of 22% in lap shear strength and 21% displacement at peak load compared with the neat PMMA spot welds, they can compete with other state-of-the-art PMMA welding techniques such as thermal bonding and ultrasonic welding, which indicates the potential of friction spot welding as an alternative fabrication technology for joining future nanocomposite engineering parts.     

Photocatalytic degradation of ciprofloxacin antibiotic in water by biosynthesized silica supported silver nanoparticles

This study reports photocatalytic degradation of ciprofloxacin (CIP) in the presence of silver nanoparticles impregnated over amorphous silica extracted from rice husk through a green approach using Melia Azedarach fruit extract. Various analyses such as X-ray diffraction analysis (XRD), Fourier-transform infrared (FTIR) spectroscopy, and field emission scanning electron microscopy (FESEM) were employed to characterize the obtained nanocomposite. Afterward, the photocatalytic activity of the nanocomposite was studied in the removal of CIP from an aqueous solution under natural sunlight irradiation. Moreover, the effect of various parameters such as solution initial pH (3–11), reaction time (30–180min), and catalyst loading (0.03–0.12 g) on degradation efficiency were studied by applying a design of experiment (DOE) methodology. The results indicated the successful synthesis and deposition of Ag nanoparticles over amorphous silica. The results of degradation experiment confirmed the acceptable performance of Ag/silica nanocomposite in photo-degradation of CIP. According to the experimental design, both catalyst loading and reaction time are highly significant; whereas the initial pH is not significant compared to other factors. Moreover, the optimal conditions were determined to be initial pH = 6.7, reaction time = 180 min, and catalyst loading of 0.12 g. By applying these optimal conditions, degradation efficiency reached to 98%. Moreover, the results of kinetic study revealed that the photo-degradation of CIP in presence of Ag/silica nanocomposite obeys a first-order kinetic model. The Ag/silica nanocomposite exhibited a high level of stability as the nanocomposites could preserve their stability after three sequential degradation cycles.     

Highly dispersed nanosilica-epoxy resins with enhanced mechanical properties

Epoxy-nanocomposite resins filled with 12-nm spherical silica particles were investigated for their thermal and mechanical properties as a function of silica loading. The nanoparticles were easily dispersed with minimal aggregation for loadings up to 25 wt% as determined using transmission electron microscopy (TEM) and ultra-small-angle X-ray scattering (USAXS). A proportional decrease in cure temperatures and glass transition temperature (for loadings of 10 wt% and above) was observed with increased silica loading. The morphology determined by USAXS is consistent with a zone around the silica particles from which neighboring particles are excluded. The “exclusion zone” extends to 10× the particle diameter. For samples with loadings less than 10 wt%, increases of 25% in tensile modulus and 30% in fracture toughness were obtained. More highly loaded samples continued to increase in modulus, but decreased in strength and fracture toughness. Overall, the addition of nanosilica is shown as a promising method for property enhancement of aerospace epoxy composite resins.     

Cure Characteristics and Mechanical Properties of HRH Bonded Nylon-6 Short Fiber-Nanosilica-Acrylonitrile Butadiene Rubber Hybrid Composite

Nano silica was synthesized by acid hydrolysis of sodium silicate using diluted hydrochloric acid. This synthetic nanosilica was used in place of hydrated silica in a HRH (hexamethylenetetramine, resorcinol and silica) bonding system for acrylonitrile butadiene rubber–nylon-6 short fiber composite. Nanosilica was also used as a reinforcing filler in acrylonitrile butadiene rubber–nylon-6 short fiber hybrid composite. Cure characteristic and mechanical properties of the hybrid composites were evaluated. Minimum torque, maximum torque, and cure time of the hybrid composites increased with silica loading. Cure rate increased with fiber loading and decreased with silica content. Scorch time also decreased with fiber loading and silica content. Volume fraction of rubber in a solvent-swollen sample increased with nanosilica. The efficiency of the HRH dry bonding system was improved in the presence of nanosilica. Nanosilica in the rubber composites also improved the tensile strength, modulus, and tear strength better than the conventional silica composites. Abrasion loss, hardness, resilience, and compression set properties were also better for the nano silica composites. The composites showed anisotropy in mechanical properties.     

Preparation and properties of polymerizable silica hybrid nanoparticles with tertiary amine structure

To increase the photopolymerization rate and improve the properties of UV coatings, polymerizable silica hybrid nanoparticles with tertiary amine structure were prepared. Organic compound with isocyanate group was first grafted onto the surface of nanosilica by reaction of nanosilica with isophorone diisocyanate, then the nanosilica bearing isocyanate group reacted with N,N-di(3-propionic acid, 1,4,7-trimethyl-3,6-dioxaoctane-8-yl acrylate, ester) ethanolamine synthesized from tripropylene glycol diacrylate and ethanolamine. The preparation was characterized by ¹H nuclear magnetic resonance (NMR) and Fourier transform infrared spectrometry (FT-IR). Thermogravimetric analysis (TGA) showed that the organic compounds grafted onto the silica decomposed from 256 °C to 650 °C and the grafting percentage based on nanosilica was 105%. The morphology analysis of nanosilica and modified silica by field-emission scanning electron microscopy (FE-SEM) indicated that the silica kept nanosized scale after modification, while the nanosilica dispersion was improved and formation of agglomerates unlikely. Determination of viscosities of coatings with modified nanosilica, it was found that viscosities of the coatings decreased in comparison with the viscosities of coatings with unmodified nanosilica. Compared with pure organic coating, the photopolymerization rate of coatings were faster when modified nanosilica was used from 1 wt% to 5 wt%, but slower when the loadings of modified nanosilica was 7 wt% because co-initiating effects of tertiary amine compound grafted on nanosilica counterbalanced the effects of UV scattering by silica on photopolymerization rate. The hardness and abrasive resistance of cured films also increased and improvement degree was different when the various amounts of modified nanosilica were used.     

Transparent nanocomposites with enhanced performances from poly(propylene carbonate) and silica

In this study, silica nanoparticles with a refractive index matching PPC and a diameter smaller than the visible light wavelength were chosen to prepare enhanced PPC/silica nanocomposites by a simple melt compounding method. The result exhibited all the nanocomposites possessed excellent transparency (about 90%), even in the nanocomposite with a silica content of 10 wt%. For PPC/silica nanocomposites, the percolation threshold was determined to be 7.5 wt% based on the dynamic rheological behavior and percolation theory. Moreover, the overall performance of the PPC-based nanocomposite with a silica content of 7.5% is the best. The optimal nanocomposite showed a Young's modulus of 3792 MPa, a yield strength of 46.5 MPa, a storage modulus of 3812 MPa and a highest temperature at maximum weight-loss rate (T_max, 309°C). These characteristics are very important for potential commodity applications of PPC.     

Synthesis and characterization of ceramic nanoparticles reinforced lead-free solder

Sn-0.7Cu is among the least expensive types of lead-free solders available. However, its poor mechanical properties have limited its application. In this study, Sn-Cu lead-free solder reinforced with amorphous silica (SiO₂) nanoparticles was synthesized through powder metallurgy route. Desired mixtures of raw materials was mechanically milled, compressed, sintered and extruded to prepare bulk solder samples. The samples were characterized by optical and electron microscopy as well as mechanical tests. The results showed that mechanical properties were increased by addition of SiO₂ nanoparticles to the solder matrix. Addition of 1.5 wt% ceramic reinforcement to the composite increased tensile, yield and compressive strengths up to 27%, 23% and 41%, respectively, compared to those of the monolithic sample. In addition, the ceramic nanoparticles caused an up to 50% decrease in the wetting angle between the substrate and the nanocomposite solder.