Preparation and characterization of nano‐SiO2 reinforced alginate‐based nanocomposite films (II)

Crosslinked alginate‐based nanocomposites at different SiO₂ contents were prepared successfully by blending the nano‐SiO₂ solution into low concentration alginate solution (0.5 wt %), with the alginate concentration increased step by step to the resulted concentration, in this course glycerol was used as plasticizer and 5 wt % CaCl₂ as crosslinker. The combined effect of SiO₂ content (1.5–8 wt %) on the microstructural, physical, mechanical, and optical properties of the nanocomposite films were investigated. The results showed that tensile strength and elongation was improved by about 40.33% and 89%, respectively, upon increasing the SiO₂ content to 4.5 wt %. In addition, water vapor permeability and swelling degree decreased by 19% and 16% with increasing SiO₂ content up to 8 and 4.5 wt %, respectively with respect to pure crosslinked alginate film. Thermogravimetric analysis also revealed that nano‐SiO₂ can improve the thermal stability of sodium alginate films produced by this method. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45286.     

Effect of in situ surface‐modified nano‐SiO2 on the thermal and mechanical properties and crystallization behavior of nylon 1010

Nylon 1010 composites filled with two types of surface‐modified SiO₂ nanoparticles (RNS and DNS) were prepared by melt blending. The mechanical properties of the composites were evaluated. The influences of the surface‐modified nano‐SiO₂ on the thermal stability, crystallization behavior, and microstructure of nylon 1010 were investigated by thermogravimetric analysis, differential scanning calorimetry (DSC), X‐ray diffraction, and transmission electron microscopy. And the interfacial interactions between the fillers and polymer matrix were examined using a Fourier transformation infrared spectrometer. It was found that the addition of the surface‐modified nano‐SiO₂ had distinct influences on the thermal stability, mechanical properties, and crystallization behavior of nylon 1010. RNS and DNS as the fillers had different effects on the mechanical properties of nylon 1010. The composites filled with RNS at a mass fraction of 1–5% showed increased break elongation, Young's modulus, and impact strength but almost unchanged or even slightly lowered tensile strength than the unfilled matrix. The DNS‐filled nylon 1010 composites had obviously decreased tensile strength, whereas the incorporation of DNS also contributed to the increase in the Young's modulus of nylon 1010, but less effective than RNS. Moreover, the nylon 1010 composites had better thermal stability than the neat polymer matrix, and the composites filled with RNS were more thermally stable than those filled with DNS. The difference in the crystallinity of neat nylon 1010 and its composites filled with RNS and DNS was subtle, although the surface‐modified nano‐SiO₂ could induce or/and stabilize the γ‐crystalline formation of nylon 1010. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of nano‐SiO2 on granule characteristic and fusion process of Poly(vinyl chloride‐co‐vinyl acetate)/nano‐SiO2 composite resin

Poly(vinyl chloride‐co‐vinyl acetate) (PVVA)/nano‐SiO₂ composite resin was prepared by radical suspension polymerization of the monomers in the presence of fumed nano‐SiO₂ particles premodified with γ‐methylacryloxypropyl trimethoxysilane. The cool dioctyl phthalate absorption percentage, granule porosity, and specific surface area of the composite resin were enhanced through incorporation of nano‐SiO₂ into the PVVA. Scanning electron microscope pictures showed the resin had higher porosity. PVVA/nano‐SiO₂ composite resin was mixed with pure PVC resin to form a mixture sample (polymer‐composite blend [PCB]) and the mixture was fused in the torque rheometer. The rheological test results indicated that, at a certain nano‐SiO₂ content, the fusion speed of PCB was accelerated and the fusion temperature of PCB was decreased, owing to nano‐SiO₂ dispersed evenly in the polymer matrix. When excessive nano‐SiO₂ was loaded, the fusion torque, the fusion time, and the fusion temperature of PCB were all increased. These properties are correlative to the dispersive density of nano‐SiO₂ in the polymer matrix. This study also demonstrated that the introduction of small amounts of nano‐SiO₂ into the resin increased the impact strength and tensile strength of PCB simultaneously. J. VINYL ADDIT. TECHNOL., 20:230–236, 2014. © 2014 Society of Plastics Engineers     

Nonisothermal crystallization of PP/nano‐SiO2 composites

The kinetics of nonisothermal crystallization of polypropylene (PP) containing nanoparticles of silicon dioxide (SiO₂) were investigated by differential scanning calorimetry (DSC) at various cooling rates. Several different analysis methods were used to describe the process of nonisothermal crystallization. The results showed that the Ozawa equation and Mo's treatment could describe the nonisothermal crystallization of the composites very well. The nano‐SiO₂ particles have a remarkable heterogeneous nucleation effect in the PP matrix. The rate of crystallization of PP/nano‐SiO₂ is higher than that of pure PP. By using a method proposed by Kissinger, activation energies have been evaluated to be 262.1, 226.5, 249.5, and 250.1 kJ/mol for nonisothermal crystallization of pure PP and PP/nano‐SiO₂ composites with various SiO₂ loadings of 1, 3, and 5%, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1013–1019, 2004     

Study of surface‐functionalized nano‐SiO2/polybenzoxazine composites

A series of the surface‐functionalized nano‐SiO₂/polybenzoxazine (PBOZ) composites was produced, and an attempt was made to improve the toughness of PBOZ material, without sacrificing other mechanical and thermal properties. A benzoxazine functional silane coupling agent was synthesized to modify the surface of nano‐SiO₂ particles, which were then mixed with benzoxazine monomers to produce the nano‐SiO₂‐PBOZ nanocomposites. The notched impact strength and the bending strength of the nano‐SiO₂‐PBOZ nanocomposites increase 40% and 50%, respectively, only with the addition of 3 wt % nano‐SiO₂. At the same load of nano‐SiO₂, the nano‐SiO₂‐PBOZ nanocomposites exhibit the highest storage modulus and glass‐transition temperature by dynamic viscoelastic analysis. Moreover, the thermal stability of the SiO₂/PBOZ nanocomposites was enhanced, as explored by the thermogravimetric analysis. The 5% weight loss temperatures increased with the nano‐SiO₂ content and were from 368°C (of the neat PBOZ) to 379°C or 405°C (of the neat PBOZ) to 426°C in air or nitrogen with additional 3 wt % nano‐SiO₂. The weight residue of the same nanocomposite was as high as 50% in nitrogen at 800°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of additive structure and size on SiO2 formation in polymer‐derived SiOC ceramics

Silicon oxycarbide (SiOC) ceramics with highly adjustable properties and microstructures have many promising applications in batteries, catalysis, gas separation, and supercapacitors. In this study, additive structures on the nucleation and growth of SiO₂ within SiOC ceramics are investigated by adding cyclic tetramethyl‐tetravinylcyclotetrasiloxane (TMTVS) or caged octavinyl‐polyhedral oligomeric silsesquioxane (POSS) to a base polysiloxane (PSO) precursor. The effects of the 2 additives on the polymer‐to‐ceramic transformation and the phase formation within the SiOC are discussed. POSS encourages SiO₂ nucleation and leads to more SiO₂ formation with significantly increased ceramic yield, which subsequently leads to higher specific surface of 1557 m²/g with a larger pore size of ～1.8 nm for the porous SiOC. High TMTVS content decreases both the specific surface area and pore volume of the resulting porous SiOCs. This study demonstrates a new approach of using Si‐rich additive POSS to increase the SiOC yield while maintaining or even increasing the specific surface area.     

Effect of amphoteric dispersant on the dispersion properties of nano‐SiO2 particles

An amphoteric polycarboxylate dispersant (APC) was synthesized by copolymerization of acrylic acid (AA), methacryloxyethyltrimethyl ammonium chloride (DMC), and isopentenol polyoxyethylene ether (IPEG). The molecular structure of APC was characterized by FT‐IR, ¹H‐NMR, and GPC. Effect of the dosage of APC on the rheological performance of nano‐SiO₂ suspension was investigated by measurements of the plastic viscosity. The results indicated that the best dispersion effect of APC was obtained when the dosage of APC was about 10 wt % (by the weight percent of nano‐SiO₂), which can maintain the dispersion of nano‐SiO₂ suspension uniformly for 4 h without settlement. Meanwhile, the zeta potential value on the surface of nano‐SiO₂ particles shows that the better dispersion performance of APC was attributed to the solvation water film formed by the polyoxyethylene side chains and the electrostatic repulsion formed by positively groups (C?N⁺) on the APC structure combined with ‐SiO^– groups on the surface of nano‐SiO₂ particles. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45075.     

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     

Study on the preparation and thermal shrinkage properties of nano‐SiO2/UHMWPE/HDPE blend microporous membranes

Nano‐SiO₂/UHMWPE/HDPE blend microporous membranes (NBMs) with different content of nano‐SiO₂ particles were prepared via thermally induced phase separation process. Thermogravimetric analysis was used to investigation of the amount of nano‐SiO₂ particles reserved in NBMs. This approach showed that about 59% of total content of nano‐SiO₂ particles reserved in NBMs. The formation and development of the interface pores were studied by scanning electron microscopy. NBMs performance was characterized by a variety of metrics including thermal shrinkage, melting and crystallization behavior, porosity and pore diameter, and permeability. The results indicated that nano‐SiO₂ particles served as nucleating agent increasing the crystalline of NBMs. The comprehensive properties of NBMs were optimum when the content of nano‐SiO₂ particles was 1%. Compared with pure HDPE separators, NBMs exhibit higher porosity and lower thermal shrinkage due to its high crystalline and the enrichment of UHMWPE chains. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41321.     

A novel method of hyperbranched poly(amide‐ester) modifying nano‐SiO2 and study of mechanical properties of PVC/nano‐SiO2 composites

A new method of surface chemical modification of nano‐SiO₂ was proposed in the paper. In the presence of catalyst, the active hydroxyl groups on the surface of nano‐SiO₂ reacted with AB₂‐type monomer (N,N‐dihydroxyethyl‐3‐amino methyl propionate) by one‐step polycondensation. And the product's Fourier transform infrared graphs and transmission electron microscopy (TEM) images proved that hyperbranched poly(amine‐ester) (HPAE) was grafted from nano‐SiO₂ surface successfully. Moreover, polyvinyl chloride (PVC)/modified nano‐SiO₂ composites were made by melt‐blending. The composites' structures and mechanical properties were characterized by TEM, scanning electron microscopy, and electronic universal testing machine. The results showed that nano‐SiO₂ grafted by HPAE increased obviously in dispersion in PVC matrix, and mechanical properties of PVC were effectively improved. Additionally, it was found that mechanical properties of PVC/nano‐SiO₂ composites reached the best when weight percent of nano‐SiO₂ in PVC matrix was 1%. Compared with crude PVC, the tensile strength of HPAE grafted nano‐SiO₂/PVC composite increased by 24.68% and its break elongation, flexural strength, and impact strength increased by 15.73, 4.07, and 184.84%, respectively. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Preparation of styrene‐acrylic emulsion by using nano‐SiO2 as seeds

A styrene‐acrylic/SiO₂ nanoparticle composite emulsion was prepared by using SiO₂ nanoparticles as seeds. The effect of factors such as the level of nano‐SiO₂, reaction temperature and ultrasound treatment of nano‐SiO₂ on the stability of the polymerization reaction was investigated. Water‐resistance of the emulsion was measured. The level of nano‐SiO₂ in the emulsion was determined by inductively coupled plasma (ICP) spectrometry. The particle morphology of the emulsion with nano‐SiO₂ was observed with transmission electron microscopy (TEM). The kinetics of the polymerization was also studied at various temperatures and various levels of nano‐SiO₂. They showed that the level of nano‐SiO₂ and reaction temperature had a great influence on the monomer conversion, particle size, coagulum content and viscosity of the emulsion. Nano‐SiO₂ treated by ultrasonics can increase the coagulum content greatly, but it does not improve the water resistance of the emulsion. The level of nano‐SiO₂ in the emulsion was lower than the theoretical value. The reaction kinetics indicated that the level of nano‐SiO₂ had less influence on the reaction rate than the reaction temperature. Even a small amount of nano‐SiO₂ can decrease the reaction rate. Copyright © 2004 Society of Chemical Industry     

The tribological properties of benzoxazine‐bismaleimides composites with functionalized nano‐SiO2

To improve the tribological properties of benzoxazine (BOZ) resin, bismaleimides (BMI) resin is chosen as organic phase, hyperbranched polysilane functionalized SiO₂ nanoparticles (HBPSi‐SiO₂) are chosen as inorganic modifiers to prepare HBPSi‐SiO₂/BOZ‐BMI composites using high shear and ultrasonic processes. The effect of content of HBPSi‐SiO₂ on the mechanical properties and tribological properties of the composites are investigated. The results show that suitable addition of HBPSi‐SiO₂ can largely enhance the impact strength, reduce the friction coefficient, and wear rate of BOZ‐BMI resin. Scanning electron microscopy is employed to research the wearing mechanism of materials. The severe wear of the BOZ pure resin is owing to fatigue wear, and the moderate wear of BOZ‐BMI resin is attributed to adhesive wear. While, the mild wear of the composites with HBPSi‐SiO₂ is due to abrasive wear. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization of acrylic latex/nano‐SiO2 composites

Acrylic/nano‐silica composite latexes were prepared by blending via high shear stirring (SS) or ball milling (BM) and in situ polymerization (IS). For comparison, composites filled with micro‐silica were also prepared. The mechanical and optical properties of the polymers formed by the composite latex filled with nano‐ or micro‐silica were investigated using an Instron testing machine, by dynamic mechanical analysis, ultraviolet–visible spectrophotometry and transmission electron micrography. The results showed that SS and BM methods could obtain better nanocomposite latex and polymers than the IS method, characterized by better dispersion of nanoparticles, higher tensile strength and T_g for SS and BM than for IS. The increase in absorbance and reduction in transmittance of UV (290–400 nm wavelength) were observed as nano‐silica content increased, whereas the UV absorbance or transmittance basically were kept unchanged for the composites filled with micro‐silica. © 2002 Society of Chemical Industry     

Water‐dispersible conducting polyaniline/nano‐SiO2 composites without any stabilizer

A water‐dispersible conducting polyaniline/ nano‐SiO₂ composite, with a conductivity of 0.071 S cm^?1 at 25°C, was prepared by the oxidative polymerization of aniline in the presence of amorphous nano‐SiO₂ particles. And the structure, morphology, thermal stability, conductivity, and electroactivity of this composite were also investigated. This composite has been steadily dispersed in the aqueous solution for about 10–36 h without the need for any stabilizer. It would significantly impulse the commercial applications of conducting polyaniline/nano‐SiO₂ composite as fillers for antistatic and anticorrosion coatings. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nanocomposites of a bismaleimide resin with octaphenylsilsesquioxane or nano‐SiO2

Nanocomposites were prepared from the resin of 4,4′‐bismaleimido‐diphenylmethane (BDM) with dipropargyl ethers of hexafluorobisphenol A (DPBPF) and octaphenylsilsesquioxane (OPS) or nano‐SiO₂. The nanocomposites were characterized by Fourier transform infrared spectroscopy, scanning electron microscope, dynamic mechanical analysis and thermogravimetric analysis. The results exhibited that OPS or nano‐SiO₂ particles could be easily dispersed in the nanocomposites and the glass transition and decomposition temperatures of c‐BDM‐DPBPF‐OPS and c‐BDM‐DPBPF‐SiO₂ nanocomposites were higher than those of c‐BDM‐DPBPF resin. The reinforcement of OPS was more effective than that of nano‐SiO₂ in the nanocomposites. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Rare‐earth‐doped SiO2‐CaF2 glass ceramic nano‐particle with upconversion properties

Rare‐earth‐doped upconversion nano‐phosphor shows new possibilities in the field of bioimaging because of its unique properties like higher penetration depth, low signal to noise ratio (SNR), good photo stability, and zero auto fluorescence. The oxyfluoride glass system is the combination of both fluoride and oxide where fluoride host offers high optical transparency due to low phonon energy and oxide network offers high physical stability. Thus, in the present work, an attempt has been made to synthesize 1 mol% Er³⁺ doped SiO₂‐CaF₂ glass ceramic nano‐particles through sol‐gel route. The synthesized glass ceramic particles were heat treated at 4 different temperatures starting from 600°C to 900°C.The X‐ray diffraction (XRD) analysis and Transmission electron microscopy (TEM) analysis confirmed the formation of CaF₂ nano‐crystals in the matrix which is 20‐30 nm in size. The vibrational spectroscopic analysis of the glass ceramics sample has been investigated by Fourier transform infrared (FTIR) spectroscopy. The UV‐Visible‐NIR spectroscopy analysis was carried out to analyze the absorption intensity in the near infrared region. Upon 980 nm excitation, the sample shows red emission corresponds to ⁴F_9/2→⁴I_15/2 energy level transition. The prepared nano‐particles showed excellent biocompatibility when tasted on MG‐63 osteoblast cells.     

Comprehensive high‐performance epoxy nanocomposites co‐reinforced by organo‐montmorillonite and nano‐SiO2

Comprehensive high‐performance epoxy nanocomposites were successfully prepared by co‐incorporating organo‐montmorillonite (o‐MMT) and nano‐SiO₂ into epoxy matrix. Because of the strong interaction between nanoscale particles, the MMT layers were highly exfoliated, and the exfoliated nanoscale MMT monoplatelets took an interlacing arrangement with the nano‐SiO₂ particles in the epoxy matrix, as evidenced by X‐ray diffraction measurement and transmission electron microscopy inspection. Mechanical tests and thermal analyses showed that the resulting epoxy/o‐MMT/nano‐SiO₂ nanocomposites improved substantially over pure epoxy and epoxy/o‐MMT nanocomposites in tensile modulus, tensile strength, flexural modulus, flexural strength, notch impact strength, glass transition temperature, and thermal decomposition temperature. This study suggests that co‐incorporating two properly selected nanoscale particles into polymer is one pathway to success in preparing comprehensive high‐performance polymer nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Sound absorption properties of polyurethane/nano‐silica nanocomposite foams

In this study, polyurethane (PU)/nano‐silica nancomposite foams were prepared. The effects of isocyanate index, cell size, density, and molecular weight of polyols on the sound absorption ratio of PU/nano‐silica foams were investigated. With increasing nano‐silica content, the sound absorption ratio of PU/nano‐silica foams increases over the entire frequency range investigated in this study. Decrease of isocyanate index, cell size, and increase of density leads to the increase of sound absorption ratio of PU/nano‐silica foams. PU/nano‐silica foams have a broad T_g centered around room temperature by decreasing molecular weight of polyol resulting in good sound absorbing ability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The influence of silane treatment on nylon 6/nano‐SiO2 in situ polymerization

Silane treatment has been applied to the preparation of nylon 6/nano‐SiO₂ composites through in situ polymerization. The influence of such treatment on the reactivity of silica, polymerization of nylon 6, and the mechanical properties of the achieved composites has been studied. Fourier transform infrared (FTIR) spectroscopy and thermal gravimetric analysis (TGA) of silicas isolated from the composites have shown that the conversion of surface silanol groups to amino and epoxy groups did not cause a significant change in the reactivity of silica and that the percentage of silica surface grafting was around 15% for all treated and untreated silicas. End group analysis has shown that the presence of silica (pretreated or not) in the composite system resulted in the decrease of the average molecular weight of the polymer matrix. However, dynamic mechanical analysis and mechanical tests revealed that treating silica with silane improved the strength and toughness of the composite materials, while untreated silica improved their strength at the expense of toughness. This can be attributed to the existence of the flexible interlayer introduced by silane treatment. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 827–834, 2002; DOI 10.1002/app.10349     

Synthesis of Al2O3/SiO2 nano‐nano composite ceramics under high pressure and its inverse Hall–Petch behavior

We report the synthesis of alumina/stishovite nano‐nano composite ceramics through a pressure‐induced dissociation in Al₂SiO₅ at a pressure of 15.6 GPa and temperatures of 1300°C‐1900°C. Stishovite is a high‐pressure polymorph of silica and the hardest known oxide at ambient conditions. The grain size of the composites increases with synthesis temperature from ~15 to ~750 nm. The composite is harder than alumina and the hardness increases with reducing grain size down to ~80 nm following a Hall–Petch relation. The maximum hardness with grain size of 81 nm is 23 ± 1 GPa. A softening with reducing grain size was observed below this grain size down to ~15 nm, which is known as inverse Hall–Petch behavior. The grain size dependence of the hardness might be explained by a composite model with a softer grain‐boundary phase.