Preparation and characterization of polymer/silica nanocomposites via double in situ miniemulsion polymerization

Polymer/SiO₂ nanocomposite microspheres were prepared by double in situ miniemulsion polymerization in the presence of methyl methacrylate, butyl acrylate, γ‐methacryloxy(propyl) trimethoxysilane, and tetraethoxysilane (TEOS). By taking full advantage of phase separation between the growing polymer particles and TEOS, inorganic/polymer microspheres were fabricated successfully in a one‐step process with the formation of SiO₂ particles and the polymerization of organic monomers taking place simultaneously. The morphology of nanocomposite microspheres and the microstructure, mechanical properties, thermal properties, and optical properties of the nanocomposite films were characterized and discussed. The results showed that hybrid microspheres had a raspberry‐like structure with silica nanoparticles on the shells of polymer. The silica particles of about 20 nm were highly dispersed within the nanocomposite films without aggregations. The transmittance of nanocomposite film was comparable to that of the copolymer film at around 70–80% from 400 to 800 nm. The mechanical properties and the fire‐retardant behavior of the polymer matrix were improved by the incorporation of silica nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3128–3134, 2010     

In situ prepared PBSu/SiO2 nanocomposites. Study of thermal degradation mechanism

A series of nanocomposites consisted of poly(butylene succinate) (PBSu) and fumed silica nanoparticles (SiO₂) were prepared using the in situ polymerization technique. The amount of SiO₂ used directly affected the final molecular weight of the prepared polyesters. At a low SiO₂ content (0.5 wt.%) the molecular weight obtained was higher compared to neat PBSu, however at higher concentrations this was gradually reduced. The melting point of the matrix remained unaffected by the addition of the nanoparticles, in contrast to the crystallinity, which was dramatically reduced at higher SiO₂ contents. This was mainly due to the extended branching and cross-linking reactions that took place between the carboxylic end groups of PBSu and the surface silanols of the nanoparticles. Thermal degradation of the PBSu/SiO₂ nanocomposites was studied by determining theirs mass loss during heating. From the variations of the activation energies, calculated from the thermogravimetric curves, it was clear that nanocomposites containing 1 wt.% SiO₂ content had a higher activation energy compared to pure PBSu, indicating that the addition of the nanoparticles could slightly increase the thermal stability of the matrix. However, in PBSu/SiO₂ nanocomposite containing 5 wt.% SiO₂ the activation energy was smaller. This phenomenon should be attributed to the existence of extended branched and cross-linked macromolecules, which reduce the thermal stability of PBSu, rather than to the addition of fumed silica nanoparticles.     

Compatibilisation effect of PP-g-MA copolymer on iPP/SiO2 nanocomposites prepared by melt mixing

In the present study, a series of iPP/SiO₂ nanocomposites, containing 1, 2.5, 5, 7.5, 10 and 15 wt% SiO₂ nanoparticles, were prepared by melt mixing in a twin screw co-rotating extruder. Poly(propylene-g-maleic anhydride) copolymer (PP-g-MA) containing 0.6 wt% maleic anhydride content was added to all nanocomposites at three different concentrations, 1, 2.5 and 5 wt%, based on silica content. Mechanical properties such as tensile strength at break and Young’s modulus were found to increase and to be mainly affected by the content of silica nanoparticles as well as by the copolymer content. For the tensile strength at break as well as for yield point, a maximum was observed, corresponding to the samples containing 2.5-5 wt% SiO₂. At higher concentrations, large nanosilica agglomerates are formed that have as a result a decrease in tensile strength. Young’s modulus increases almost linearly on the addition of SiO₂, and takes values up to 60% higher than that of neat iPP. Higher concentrations of PP-g-MA resulted in a further enhancement of mechanical properties due to silica agglomerate reduction. This finding was verified from SEM and TEM micrographs. Evidently the surface silica hydroxyl groups of SiO₂ nanoparticles react with maleic anhydride groups of PP-g-MA and lead to a finer dispersion of individual SiO₂ nanoparticles in the iPP matrix. The enhanced adhesion in the interface of the two materials, as a result of the mentioned reaction, has been studied and proved by using several equations. The increased Vicat point of all nanocomposites, by increasing the PP-g-MA content, can also be mentioned as a positive effect.     

Nanocomposite films based on cellulose reinforced with nano-SiO2: microstructure, hydrophilicity, thermal stability, and mechanical properties

Microcrystalline cellulose/nano-SiO₂ composite films have been successfully prepared from solutions in ionic liquid 1-allyl-3-methylimidazolium chloride by a facile and economic method. The microstructure and properties were investigated by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, scanning electron microscopy, transmission electron microscopy, water contact angle, thermal gravimetric analyses, and tensile testing. The results revealed that the well-dispersed nanoparticles exhibit strong interfacial interactions with cellulose matrix. The thermal stability and tensile strength of the cellulose nanocomposite films were significantly improved over those of pure regenerated cellulose film. Furthermore, the cellulose nanocomposite films exhibited better hydrophobicity and a lower degree of swelling than pure cellulose. This method is believed to have potential application in the field of fabricating cellulose-based nanocomposite film with high performance, thus enlarging the scope of commercial application of cellulose-based materials.     

UV‐cured polyester‐acrylate nanocomposite films with silane‐grafted silica nanoparticles

UV‐curing technique was employed in this study to prepare polyester‐acrylate nanocomposite films with silane‐grafted silica nanoparticles. Methacryloxypropyl trimethoxysilane was grafted to the surfaces of silica nanoparticles to improve dispersion of silica nanoparticles as well as interfacial adhesion between the resin matrix and silica nanoparticles. The silane‐grafting was confirmed by nuclear magnetic resonance and infrared spectroscopy. The effects of the silane‐grafting on the mechanical and optical properties as well as UV‐curing behavior of the nanocomposite films were investigated. The tensile strength, transmittance, UV‐curing rate, and final chemical conversion of the nanocomposite films were increased by use of the grafted silica nanoparticles as compared to the use of neat silica nanoparticles. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrogen Bonding in Polyurethane-Silica Nanocomposites

Thin films of polyester-based polyurethane-silica nanocomposites with 34% hard segments and different concentrations of nano SiO₂ filler (0, 0.5, 1.0 and 3 vol.%) have been prepared. The hydrogen bonding and orientational behaviour of hard and soft segments were analysed using infrared linear dichroic measurements. The number of hydrogen bonded NH and CO groups and orientation function were calculated from polarized FTIR spectra. The presence of nanosilica slightly increased the number of hydrogen bonded carbonyls. The soft segments in nanocomposite films display increased orientation in comparison to the neat polymer film. The addition of 3% nanosilica significantly reduced elongation at break. The results were compared with hydrogen bonding and orientational behaviour of thin film of polyether-based silica nanocomposites.     

Moisture and solvent responsive cellulose/SiO<Subscript>2</Subscript> nanocomposite materials

Water responsive SiO₂/cellulose nanocomposite hydrogels and films were constructed, for the first time, by dispersing SiO₂ nanoparticles into cellulose solution in LiOH/urea solvent, and then by crosslinking with epichlorohydrin or regeneration in coagulation bath, respectively. The cellulose nanocomposite materials were characterized by Field emission scanning electron microscopy, FTIR, dynamic rheology, wide angle X-ray diffraction and mechanical test. The SiO₂/cellulose nanocomposites at wet state or in water displayed unique behaviors, showing higher light transmittance than those before contacting with water. The results revealed that strong hydrogen-bonding interaction among water, cellulose and SiO₂ led the good dispersion of SiO₂ nanoparticles in the cellulose matrix. The incorporation of SiO₂ nanoparticles improved the transmittance and mechanical strength of the cellulose hydrogels, and also enhanced the mechanical strength of the films. Especially, the cellulose/SiO₂ nanocomposite films were milky at dry state, and changed to transparent after being soaked in water, different from the cellulose film without the SiO₂ nanoparticles. In our findings, SiO₂ and cellulose with water could form strong hydrogen bonding to create a homogenous network structure. The cellulose/SiO₂ composite as a smart material exhibited moisture and solvent responsiveness, showing potential applications in moisture detection.     

Ultrasonically assisted in situ emulsion polymerization: a facile approach to prepare conducting copolymer/silica nanocomposites

Ultrasonically assisted in situ emulsion polymerization was used to prepare electrically conducting copolymer poly(aniline‐co‐p‐phenylenediamine) [poly(Ani‐co‐pPD)] and silica (SiO₂) nancomposites. This approach can solve problems in the dispersion and stabilization of SiO₂ nanoparticles in the copolymer matrix. It was found that the aggregation of SiO₂ nanoparticles could be reduced under ultrasonic irradiation. Scanning transmission electron microscopy (STEM) confirmed that the resulting poly(Ani‐co‐pPD)/SiO₂ nanocomposite particles were spherical in shape, in which SiO₂ nanoparticles were well dispersed. The comonomer molecules were absorbed on the surface of SiO₂ particles and then polymerized to form core–shell nanocomposite. The incorporation of SiO₂ in the nanocomposite was supported by Fourier transform infrared spectroscopy (FT‐IR). UV‐visible spectra of the diluted colloid dispersion of nanocomposite particles were similar to those of the neat copolymer. Conductivity of nanocomposites was higher than the value obtained for the neat copolymer. Copyright © 2009 John Wiley & Sons, Ltd.     

Hydrogen bonding and mechanical properties of thin films of polyether-based polyurethane-silica nanocomposites

Two series of thin films of polyether-based polyurethane-silica nanocomposites having hard segment content of 51% and 34% and different concentrations of SiO₂ nanoparticles (0, 0.5, 1.0 and 3.0 vol.%) have been prepared. Infrared linear dichroic (LDIR) ratio, mechanical and differential scanning calorimetry (DSC) measurements were performed in order to determine the influence of hydrogen bonding on their mechanical and thermal properties. The degree of phase separation (DPS) and orientational functions in dependence on strain were calculated from the polarized IR spectra. The presence of silica nanoparticles gives rise to significant differences in the mechanical (stress-strain) properties of the nanocomposites with regard to the pure polymer. The nanocomposite thin films with lower hard segment content (HSC) displayed decreased stiffness and tensile and increased elongation at break in comparison to the nanocomposites with higher HSC. There was no distinctive influence of nanoparticles on the glass transition temperatures of soft segments. Nanosilica significantly affected the melting behavior of the hard phase only in samples with higher HSC.     

Hydrophilic nature and sorption-diffusion properties of nanocomposite hybrid polysulfone films

Hybrid nanocomposite films containing silica (??11.4 wt.%) or titania (??18.8 wt.%) in the polymer matrix were prepared by the sol-gel method using the hydrolytic polycondensation of tetraethoxysilane and tetrabutoxysilane in a THF solution of aromatic polymer, polysulfone (PSF). The influence of the oxide nature and the film composition on the structure, the interaction of the polymer with oxides, hydrophilicity, and sorption-diffusion properties of the hybrid films were studied by FTIR spectroscopy, atomic force microscopy, dynamic light scattering, and a complex of other physicochemical methods. The absence of chemical or intermolecular hydrogen bonds between the polymer and oxide particles in the PSF films was shown. The average size of the oxides (SiO₂, ??20 nm; TiO₂, ??90 nm) in the films and roughness of their surface (??0.2?C0.8 nm) were determined. The introduction of oxides into the polymer matrix increases the hydrophilic properties and the ability of the PSF films to swell in water; the diffusion coefficients of water and permeability of water vapor in the PSF films also increase. Titania also induces a more considerable change in the structure of the polymer matrix and more strongly affects the sorption-diffusion properties of the hybrid films in aqueous solutions of THF. All prepared nanocomposite films PSF/SiO₂ and PSF/TiO₂ are capable of extracting an organic component from aqueous solutions and can be used as sorbents and membrane films for the removal of organic substances from the aqueous medium.     

Investigating properties of poly (ether‐amide)/MWCNT nanocomposite films containing 2,7‐bis(4‐aminophenoxy)naphthalene and isophthalic segments

Three nanocomposite films based on aramid (poly (ether‐amide), PEA) and multiwall carbon nanotubes (MWCNT) were prepared via solution casting method using 2,7‐bis(4‐aminophenoxy)naphthalene (4) and isophthalic acid (5) containing various amounts of MWCNT (2, 3, 5 wt.%). To comprehensively analyze the properties of the cast films as well as the monomers, different techniques were employed, namely FT‐IR, ¹H NMR, X‐ray diffraction, and field emission scanning electron microscopy. Also, thermal and tensile properties of PEA (6) and nanocomposite films were investigated using thermogravimetric analysis and mechanical analysis, respectively. The morphology, thermal, and mechanical properties of nanocomposite films approved that MWCNT had well dispersion in the PEA matrix and showed a synergistic effect on improving all of the investigated properties. Based on the thermogravimetric analysis results, employing MWCNT caused to increase in the char yields from 61 (in the neat PEA) to 66 (in the PEA /MWCNT nanocomposite 5 wt.%) under the nitrogen atmosphere. In comparison to the pristine PEA (426°C), the temperature at 10 losses mass % (T₁₀) was increased from 530°C to 576°C, with 2 to 5 wt.% of MWCNT. Mechanical analysis revealed that the tensile strength and initial modulus were improved by incorporating MWCNT into PEA (81.70–93.40 MPa and 2.10–2.22 GPa, respectively). Electrical conductivity of the PEA/MWCNT nanocomposites was displayed maximum value in the 5 wt.%, showing satisfactory value in many application areas. The X‐ray diffraction technique was employed to study the crystalline structure of the prepared nanocomposite films as well as PEA. In addition, the electrochemical impedance spectroscopy study demonstrated that the prepared nanocomposites had significant impedance improvement in the presence of MWCNTs.     

Enhancing mechanical and thermal properties of PLLA ligaments with fumed silica nanoparticles and montmorillonite

Nanocomposites of poly(l-lactic acid) (PLLA) containing 2.5 wt% of fumed silica nanoparticles (SiO₂) and organically modified montmorillonite (OMMT) were prepared by solved evaporation method. From SEM micrographs it was observed that both nanoparticles were well dispersed into PLLA matrix. All nanocomposites exhibited higher mechanical properties compared to neat PLLA, except elongation at break, indicating that nanoparticles can act as efficient reinforcing agents. Nanoparticles affect, also, the thermal properties of PLLA and especially the crystallization rate, which in all nanocomposites is faster than that of neat PLLA. From the thermogravimetric curves it can be seen that neat PLLA nanocomposites present a relatively better thermostability than PLLA, and this was also verified from the calculation of activation energy (E). From the variation of E with increasing degree of conversion it was found that PLLA/nanocomposites decomposition takes place with a complex reaction mechanism, with the participation of two different mechanisms. The combination of models, nth order and nth order with autocatalysis (Fn–Cn), for PLLA and PLLA/OMMT as well as the combination of Fn–Fn for PLLA/SiO₂ give the better results. For the PLLA/OMMT the values of the E for both mechanisms are higher than neat PLLA. For the PLLA/SiO₂ nanocomposite the value of the E is higher than the corresponding value for PLLA, for the first area of mass loss, while the E of the second mechanism has a lower value.     

Mechanical and Electrochemical Properties of New Nanocomposite Polymer Electrolytes Based on Poly(vinylidene fluoride-co-hexafluoropropylene) and SiO<Subscript>2</Subscript> Addition

Nanocomposite polymer electrolytes based on the system poly(vinylidene fluoride-co-hexafluoropropylene)–liquid electrolyte 1 mol/L LiBF₄ in gamma-butyrolactone which is modified by introducing up to 10 wt % of SiO₂ nanopowder (an average particle size of 7 nm) are synthesized and characterized. The introduction of SiO₂ nanoparticles worsens the elasticity of films but increases their fracture stress to 24 MPa. The conductivity of the nanocomposite electrolytes containing SiO₂ nanoparticles is higher than that without SiO₂ and attains 3.7 mS/cm at 20°C for the electrolyte containing 1.25 wt % SiO₂. Upon the introduction of SiO₂ nanoparticles, the electrochemical stability of electrolytes grows by 0.50–0.85 V and attains 6.7 V relative to Li/Li⁺.     

The synthesis and characteristic study of 6FDA-6FHP-NLO polyimide/SiO2 nanohybrid materials

Hybrid nanocomposite films of silica (SiO₂) in polyimide (PI) from 4,4^′-(hexafluoroisopropylidene) diphthalic arhydride (6FDA), 2,2-Bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6FHP) and nonlinear optical (NLO) molecule have been successfully fabricated by an in situ sol-gel process. The silica content in the hybrid films was varied from 0 to 22.5 wt%. These nanocomposite films exhibit fair good optical transparency. Fourier transform infrared (FTIR) spectroscopy results confirm the formation of SiO₂ particles in PI matrix. Scanning electron microscope (SEM) images show that the SiO₂ phase is well dispersed in the polymer matrix. Their glass transition behavior and thermal stability were investigated by differential scanning calorimeter (DSC) and thermal gravimetric analysis (TG).     

Preparation of poly(vinylidene fluoride) nanocomposite membranes based on graft polymerization and sol–gel process for polymer electrolyte membrane fuel cells

Proton conducting nanocomposite membranes consisting of poly(vinylidene fluoride-co-chlorotrifluoroethylene)-graft-poly(styrene sulfonic acid), i.e., P(VDF-co-CTFE)-g-PSSA graft copolymer and sulfonated silica and were prepared using a sol–gel reaction and subsequent oxidation of a silica precursor, i.e., (3-mercaptopropyl) trimethoxysilane (MPTMS). The successful formation of amorphous phase nanocomposite membranes was confirmed via FT-IR and wide-angle X-ray scattering. All membranes were semi-transparent and mechanically strong, as characterized by a universal tensile machine. Transmission electron microscopy and small-angle X-ray scattering analysis revealed that silica 5–10 nm in size were homogeneously dispersed in the matrix at up to 5 wt.% of MPTMS. At higher concentrations, the silica grew to more than 50 nm in size, which disrupted the microphase-separated structure of the graft copolymer. As a result, both proton conductivity (0.12 S/cm at 25 °C) and single cell performance (1.0 W/cm² at 75 °C) were maximal at 5 wt.% MPTMS.     

Effect of different nanoparticles on HDPE UV stability

In the present study different series of HDPE nanocomposites were prepared by melt mixing on a Haake-Buchler Reomixer, containing 2.5 wt% of multiwall carbon nanotubes, pristine and modified montmorillonite, and SiO₂ nanoparticles. Nanocomposites in the form of thin films were exposed to UV irradiation at 280 nm at constant temperature (25 °C) and constant relative humidity (50%) for several times. From tensile strength and Young’s Modulus measurements it was verified a high increase with initial UV irradiation times (till 100 h) and a slight reduction thereafter. The increase was higher in nanocomposites compared with neat HDPE, except these containing MWCNTs, and was attributed to the crystallinity increase in the particular samples. The mechanical properties reduction at higher UV irradiation times was attributed to the extensive macromolecular chain scission causing irregularities and holes in film surfaces. However, from FTIR study it was found that SiO₂ and organically modified montmorillonite cause a serious effect on HDPE during UV degradation. New chemical compounds containing carbonyl, vinyl and hydroxyl groups were formed. It seems that these nanoparticles have an accelerating effect acting as catalysts to HDPE photo-oxidation. This was also verified from micro-Raman analysis. Untreated montmorillonite has also a small influencing effect while neat HDPE and nanocomposites containing multiwall carbon nanotubes have the highest UV stability.     

Novel polyester/SiO2 nanocomposite membranes: Synthesis,properties and morphological studies

In this paper, a new type of soluble polyester/silica (PE/SiO₂) hybrid was prepared by the ultrasonic irradiation process. The coupling agent γ-glycidyloxypropyltrimethoxysilane (GOTMS) was chosen to enhance the compatibility between the polyester (PE) and silica (SiO₂). Furthermore, the effects of the coupling agent on the morphologies and properties of the PE/SiO₂ hybrids were investigated using UV-vis and FT-IR spectroscopies and FE-SEM. The densities and solubilities of the PE/SiO₂ hybrids were also measured. The results show that the size of the silica particle was markedly reduced by the introduction of the coupling agent, which made the PE/SiO₂ hybrid films become transparent. Furthermore, thermal stability, residual solvent in the membrane film and structural ruination of membranes were analyzed by thermal gravimetric analysis (TGA). The effects of SiO₂ nanoparticles on the glass transition temperature (T_g) of the prepared nanocomposites were studied by differential scanning calorimetry (DSC). Moreover, their mechanical properties were also characterized. It can be observed that the Young's moduli (E) of the hybrid films increase linearly with the silica content. The results obtained from gas permeation experiments with a constant pressure setup showed that adding SiO₂ nanoparticles to the polymeric membrane structure increased the permeability of the membranes.     

Crystal growth in alumina/poly(ethylene terephthalate) nanocomposite films

The crystal growth and morphology in 150‐nm‐thick PET nanocomposite thin films with alumina (Al₂O₃) nanoparticle fillers (38 nm size) were investigated for nanoparticle loadings from 0 to 5 wt %. Transmission electron microscopy of the films showed that at 1 wt % Al₂O₃, the nanoparticles were well dispersed in the film and the average size was close to the reported 38 nm. Above 2 wt % Al₂O₃, the nanoparticles started to agglomerate. The crystal growth and morphological evolution in the PET nanocomposite films kept at an isothermal temperature of 217 °C were monitored as a function of the holding time using in situ atomic force microscopy. It was found that the crystal nucleation and growth of PET was strongly dependent on the dispersed particles in the films. At 1 wt % Al₂O₃, the overall crystal growth rate of PET lamellae was slower than that of the PET homopolymer films. Above 2 wt % Al₂O₃, the crystal growth rate increased with nanoparticle loading because of heterogeneous nucleation. In addition, in these PET nanocomposite thin films, the Al₂O₃ nanoparticles induced preferentially oriented edge‐on lamellae with respect to the surface, which was not the case in unfilled PET as determined by grazing‐incidence X‐ray diffraction. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 747–757, 2007     

Synthesis and characterization of poly1-hexene/silica nanocomposites

SiO₂ nano particles, with particle size of 12 nm, were first modified by substituting surface OH groups with O-hexyl moiety. Then, poly1-hexene/modified-SiO₂ composites with various nano-SiO₂ weight fractions were prepared by three different methods: in situ, solution, and melt methods and designated as PH-SiO₂/Insitu, PH-SiO₂/Sol and PH-SiO₂/Melt, respectively. PH-SiO₂/Insitu samples showed highly uniform particle dispersion up to 30 wt. % of silica while in PH-SiO₂/Sol and PH-SiO₂/Melt samples agglomeration of the silica nanoparticles occurred for filler contents ≥5 wt. % (i.e. 5, 10, 20 and 30 wt%). In the synthesized composites, the storage modulus significantly increased as high as 20.7 times when compared with neat poly1-hexene. Maximum decomposition temperature (T_max) and char yield at 600 °C increased with increasing silica level. Rheological results showed that G^ʹ> G^ʺ over the frequency range, illustrating the elastic behavior of the composite samples. In fact, samples showed the characteristic of a non-Newtonian fluid with a strong shear thinning effect in which η* increased with increasing filler weight fraction. From the results, it can be expected that modified silica could replace silica nanoparticles in polyolefin nanocomposite reinforcement.     

Cyanate Ester/Functionalized Silica Nanocomposite: Synthesis,Characterization and Properties

In this paper silica nanoparticles with covalently grafted polymer chains were incorporated into bisphenol A dicyanate ester (BADCy) to prepare composites which resulted in improvements in the mechanical and thermal properties. Fourier‐transform infrared (FT‐IR) spectroscopy transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) were employed to examine the surface functionalization of silica nanoparticles. The effects of functionalized SiO₂ (F‐SiO₂) on the curing reactivity mechanical and thermal properties of BADCy resin were investigated systematically. The curing reaction of the system was facilitated with the addition of F‐SiO₂. Meanwhile compared with the neat resin the incorporation of appropriate content of modified F‐SiO₂ can enhance the mechanical properties including impact flexural strengths and fracture toughness K_IC of BADCy resin. In addition the thermal stability of BADCy/F‐SiO₂ nanocomposites is also superior to that of pure BADCy resin.