ENHANCED MECHANICAL PROPERTIES OF POLYPROPYLENE/SILICA NANOCOMPOSITES WITH SURFACE MODIFICATION OF NANO-SILICA VIA IN SITU COPOLYMERIZATION OF METHYL METHACRYLATE AND BUTYL ACRYLATE

Nano-sized silica particles were modified with methacryloxy-propyltrimethoxysilane(MPS) followed by in situ copolymerization of methyl methacrylate(MMA) and butyl acrylate(BA).These modified nanoparticles were compounded with polypropylene(PP) to prepare PP/silica nanocomposites.PMMA grafted on nano-silica enhances the dispersion of the nanoparticles and interfacial adhesion,decreases the size of PP spherulites in nanocomposites and leads to increasing the Young's modulus and toughness of PP/silica nanoc...     

Synthesis and Structural Analysis of Au-Doped TiO2/SiO2 Mixed Oxide Films Prepared by Sol-Gel Process

The systematic modifications of silica matrix as a function of modified Ti-alkoxide contents (Au nanocrystals doped TiO₂/SiO₂ mixed oxide thin films) have been investigated by the sol-gel process. A structural analysis on the various steps of the hydrolysis-condensation process as well as solid powder is determined by IR, UV-Visible, and ²⁹Si NMR spectroscopy. ²⁹Si MAS spectra are characterized by broad lines for the three types of sites. Different distributions (Q ², Q ³, and Q ⁴ units) observed in the TiO₂/SiO₂ (1 : 3) sample. Proper control of the process condition, modifying the Ti alkoxide as a less reactive precursor, improves the increase the amount of Ti–O–Si bonding in the silica network of TiO₂/SiO₂ mixed oxide matrices and the distribution of metal oxides. This method can be used for the preparation of homogeneous metal and metal-metal alloy nanocrystals deposition from mixed oxide thin films.     

Preparation and enhanced properties of poly(propylene)/ silica‐grafted‐hyperbranched polyester nanocomposites

A series of poly(propylene) silica‐grafted‐hyperbranched polyester nanocomposites by grafting the modified hyperbranched polyester (Boltorn? H20), possessing theoretically 50% end carboxylic groups and 50% end hydroxyl groups, which endcapped with octadecyl isocyanate (C19), onto the surface of SiO₂ particles (30 nm) through 3‐glycidoxy‐propyltrimethoxysilane (GPTS) was prepared. The effect of silica‐grafted‐modified Boltorn? H20 on the mechanical properties of polypropylene (PP) was investigated by tensile and impact tests. The morphological structure of impact fracture surface and thermal behavior of the composites were determined by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), respectively. The melt viscosity of composites was investigated by melt flow index (MFI). The obtained results showed that: (1) the modified Boltorn? H20 was successfully grafted onto the SiO₂ surface confirmed by FT‐IR and X‐ray photoelectron spectroscopy (XPS) analysis; (2) the incorporation of silica‐grafted‐modified Boltorn? H20 (3–5 wt% SiO₂) greatly enhanced the notched impact strength as well the tensile strength of the composites; (3) the incorporation of silica‐grafted‐modified Boltorn? H20 had no influence on the melting temperature and crystallinity of PP phase; (4) the MFI of PP composites increased when the silica‐grafted‐modified Boltorn? H20 particles were added compared with PP/SiO₂ or PP/SiO₂‐GPTS composites. Copyright © 2004 John Wiley & Sons, Ltd.     

Solid-State NMR Study of Phase Separation and Order of Water Molecules and Silanol Groups in Polysiloxane Networks

Homogeneity and structure of organically modified polysiloxane networks prepared by sol-gel co-condensation, as well as location and nature of water molecules and silanol groups were studied by 1D and 2D solid-state NMR. ¹H–²⁹Si and ¹H–¹H interatomic distances were estimated from variable contact-time CP/MAS experiments, ¹H NMR chemical shifts and off-resonance WISE NMR. A structure model of these networks is proposed and discussed. The fraction of proton-inaccessible units Q⁴ in the networks decreases with increasing amounts of dimethylsiloxane (D) and methylsiloxane (T) units. In contrast to systems prepared by co-condensation of tetraethoxysilane (TEOS) with dimethyl(diethoxy)silane (DMDEOS), proton-inaccessible units form essential fraction in networks prepared by co-condensation of TEOS with methyl(triethoxy)silane (MTEOS). The proton-accessible part of the networks with high O/Si ratios is nano-heterogeneous phase, which is composed of water containing Q ⁱ particles separated by copolymer domains. The overall homogeneity and uniformity of binding sites around silanol groups increases by co-condensation TEOS with DMDEOS or MTEOS, while the amount of physisorbed water as well as the hydrogen bond strength decreases, as compared with neat silica gel prepared by polycondensation of TEOS.     

Formation of an in situ nanosilica nanomatrix via graft copolymerization of vinyltriethoxysilane onto natural rubber

Natural rubber (NR) with an in situ nanosilica nanomatrix was characterized in present work. The in situ nanosilica nanomatrix was prepared via graft copolymerization of a silane monomer, vinyltriethoxysilane (VTES), onto deproteinized NR (DPNR) in latex stage using tetrapentamine (TEPA)/tert‐butylhydroperoxide (TBHPO) as initiators. VTES conversion of more than 80% was obtained, and it depended on VTES concentration. The graft copolymer structure was characterized by Fourier transform infrared (FT‐IR), solution‐state proton nuclear magnetic resonance (¹H‐NMR), and solid‐state ²⁹Si‐NMR spectroscopy. FT‐IR analysis of the graft copolymer confirmed the formation of in situ silica particles, while solution‐state ¹H‐NMR and solid‐state ²⁹Si‐NMR revealed the partial hydrolysis of the ethoxy groups and polycondensation of the silanol groups. The formation of nanosilica particles enhanced thermal and mechanical properties of the graft copolymer. Morphology observations of the in situ nanosilica nanomatrix through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the spherical nanosilica particles form a nanomatrix surrounding NR particle. The formation of the nanomatrix was proved to enhance mechanical properties for NR materials.     

Influence of downsizing of zeolite crystals on the orthorhombic ↔ monoclinic phase transition in pure silica MFI-type

The impact of crystal size on the transition orthorhombic ↔ monoclinic phase in MFI-type purely silica zeolites is investigated between 293 and 473 K using ²⁹Si MAS NMR and powder X-ray diffraction. Three silicalite-1 zeolites are synthesized: a material constituted of micron-sized crystals, pseudospherical nanometer-sized crystals and hierarchical porous zeolites with a mesoporous network created by the use of a gemini-type diquaternary ammonium surfactant giving nanosheet zeolites. Our results show for the first time that the orthorhombic ↔ monoclinic phase transition already known for micron-sized particles also occurs in nanometer-sized zeolite crystals whereas our data suggest that the extreme downsizing of the zeolite crystal to one unit cell in thickness leads to an extinction of the phase transition.     

Reactivity of Extra‐framework Species of USY Zeolites in Alkaline Medium

Zeolites of type USY (ultra‐stable Y) were obtained by steaming of NH₄NaY modification. Samples were modified by subsequent alkaline treatment in KOH solution. USY and USY‐KOH were characterised by chemical element analysis, XRD, IR, ²⁹Al and ²⁹Si MAS NMR spectroscopic measurements. Correct silicon to aluminium ratios (Si/Al) were determined by XRD and IR (double ring vibration w_DR) data whereas values calculated according to data of ²⁹Si MAS NMR and IR spectroscopy (asymmetrical TOT valence vibration w_TOT) appeared to be too high., In the latter case, the signals of the zeolite framework were strongly superimposed by that of extra‐framework silica gel (EFSi) formed during steaming. It was found that alkaline leaching induces desilication of silicon‐rich area of the zeolite framework and partial dissolution of EFSi. Silicate ions of both react with likewise dissolved extra‐framework aluminium (EFAl) to form X‐ray amorphous aluminosilicate. Consequently, the superposition of the ²⁹Si MAS NMR signals of the zeolite framework by silica gel was reduced for Q⁴(0Al) but increased for Q⁴ (2Al) and Q⁴(3Al) structure units. A reinsertion of EFAl into the zeolite framework has not been observed.     

The use of 29Si NMR to characterize the sol-gel synthesis of cordierite

 Cordierite powder was synthesized via different sol-gel procedures. The use of ²⁹Si NMR spectra of all stages beginning from tetraethoxysilane (TEOS) up to final ceramic powder material is discussed. In the early stages of the sol-gel process all oligomeric structure units can be identified. Spectra of the higher condensed sols only allow the quantification of Qⁿ-groups. MAS spectra of gels heated up to 750 °C show no fine structure to be evaluated. Spectra of samples heated to 1250 °C indicate a sluggish disorder-order transformation from hexagonal α-cordierite to orthorhombic cordierite. Received: 20 May 1996/Accepted: 25 July 1996     

Polypropylene wax (PPw)/silica hybrid by in situ non-aqueous sol–gel process for preparation of PP/silica nanocomposites

This paper presented a novel approach to prepare PP/silica nanocomposites. First, PPw-g-KH570 (γ-methacryloxypropyl trimethoxysilane) was obtained by pre-irradiation grafting method and characterized by FTIR and TGA. Then the non-aqueous sol–gel gelation kinetics of TEOS (tetraethoxysilane)-formic acid system in xylene was researched. Subsequently PPw/silica hybrid was obtained by in situ non-aqueous sol–gel reaction of TEOS in the presence of PPw-g-KH570 solution in xylene. Finally PP/silica nanocomposites were prepared by blending of PP matrix and PPw/silica hybrid. The mechanism of in situ formed PPw/silica hybrid was proposed. The morphology of PPw/silica hybrid and microstructures of PP/silica nanocomposites were characterized by TEM and SEM. The mechanical and thermal properties of PP/silica nanocomposites were also well studied by tensile tests and DSC. It was showed that the nanosilica particles were well dispersed in PPw/silica hybrid with the aid of grafting KH570 due to co-condensation by grafted KH570 and TEOS. PPw/silica hybrid was well dispersed in PP matrix with good compatibility and strong interactions. The resulted PP/silica nanocomposites possessed better performance than that of pure PP matrix.     

Correlations between data of <Superscript>29</Superscript>Si NMR and thermogravimetry for silica/monetite nanocomposites

Silica/monetite nanocomposites were synthesized through controlled hydrolysis of tetraethoxysilane at concentrations of 5, 10, 15, and 20% mol/mol of calcium phosphate forming the solids named CaPSil1, CaPSil2, CaPSil3, and CaPSil4, respectively. XRD patterns showed formation of nanocomposites with a decrease in crystallinity. The NMR ²⁹Si spectra suggested an increase in the content of incorporated silica with reduction of Q³ (–SiOH) signal, which contributes for mass loss, in agreement with thermogravimetry. The incorporation of silica increased the chemical stability of the precursor phosphate in an acidic medium.     

Synthesis, characterization and thermal properties of novel epoxy containing silicon and phosphorus nanocomposites by sol-gel method

Organic-inorganic hybrids were prepared using diglycidyl ether of bisphenol A (DGEBA) type epoxy and tetraethoxysilane via the sol-gel process. The DGEBA type epoxy was modified by a coupling agent to improve the compatibility of the organic and inorganic phases. The sol-gel technique was used successfully to incorporate silicon and phosphorus into the network of hybrids increasing flame retardance.Fourier transform infrared spectroscopy and ²⁹Si nuclear magnetic resonance spectroscopy were used to characterize the structure of the hybrids. In condensed siloxane species for TEOS, silicon atoms through mono-, di-, tri-, and tetra-substituted siloxane bonds are designated as Q¹, Q², Q³, Q⁴, respectively. For 3-isocyanatopropyltriethoxysilane and diethylphosphatoethyltriethoxysilane, mono-, di-, tri-, tetra-substituted siloxane bonds are designated as T¹, T², T³. Results revealed that Q⁴, Q³, T³ are the major environments forming a network structure. The morphology of the ceramer was examined by scanning electron microscopy and Si mapping. Particle sizes were below 100 nm. The hybrids were nanocomposites. The char yield of pure epoxy resin was 14.8 wt.% and that of modified epoxy nanocomposite was 31 wt.% at 800 °C. A higher char yield enhances the flame retardance. Values of limiting oxygen index of pure epoxy and modified epoxy nanocomposites are 24 and 32, respectively, indicating that modified epoxy nanocomposites possess better flame retardance than the pure epoxy resin.     

Synthesis of Mesoporous Silica Immobilized with 3-[(Mercapto or amino)propyl]trialkoxysilane by a Simple One-pot Reaction

Sodium silicate from rice husk ash (RHA) was transformed to functionalized silica with 3‐(mercaptopropyl)‐trimethoxysilane (MPTMS) or 3‐(aminopropyl)triethoxysilane (APTES) via a simple sol‐gel technique in a one‐pot synthesis to give RHAPrSH and RHAPrNH₂. The ²⁹Si MAS NMR of RHAPrSH and RHAPrNH₂ showed the presence of T¹, T², T³, Q², Q³ and Q⁴ silicon centers. The ¹³C MAS NMR showed that RHAPrSH had chemical shifts at δ 16.59, 32.73, consistent with two of the carbon atoms of the MPTMS moiety, while the ¹³C MAS NMR of RHAPrNH₂ had chemical shifts at δ 14.58, 26.13, 47.87, consistent with the three carbon atoms of the APTES moiety. The presence of carbon, silicon, sulfur and nitrogen in RHAPrSH and RHAPrNH₂ was determined by a combination of elemental analysis and EDX study.     

Polypropylene/montmorillonite nanocomposites toughened with SEBS‐g‐MA: Structure–property relationship

Polypropylene (PP)/organo‐montmorillonite (Org‐MMT) nanocomposites toughened with maleated styrene‐ethylene‐butylene‐styrene (SEBS‐g‐MA) were prepared via melt compounding. The structure, mechanical properties, and dynamic mechanical properties of PP/SEBS‐g‐MA blends and their nanocomposites were investigated by X‐ray diffraction (XRD), polarizing optical microscopy (POM), tensile, and impact tests. XRD traces showed that Org‐MMT promoted the formation of β‐phase PP. The degree of crystallinity of PP/SEBS‐g‐MA blends and their nanocomposites were determined from the wide angle X‐ray diffraction via profile fitting method. POM experiments revealed that Org‐MMT particles served as nucleating sites, resulting in a decrease of the spherulite size. The essential work of fracture approach was used to evaluate the tensile fracture toughness of the nanocomposites toughened with elastomer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3112–3126, 2005     

Covalent grafting of organoalkoxysilanes on silica surfaces in water-rich medium as evidenced by <Superscript>29</Superscript>Si NMR

This paper addresses two questions related to functionalization of silica particles: (1) is the grafting of hydrophobic organoalkoxysilanes on a silica surface possible in water-rich medium and (2) how to prove the formation of covalent bonds with the surface? Trimethylethoxysilane, dimethyldiethoxysilane and methyltriethoxysilane have been reacted with precipitated silica in water-rich medium (water/ethanol 25/75 v/v) and ²⁹Si MAS NMR was used to answer both questions: ²⁹Si chemical shift values of the organosilicon units in the case of trimethylethoxysilane and dimethyldiethoxysilane clearly distinguished between self-condensation reactions and surface reactions through covalent bonds.     

Preparation of Thick Films by Electrophoretic Deposition Using Surface Modified Silica Particles Derived from Sol-Gel Method

Thick films were prepared by the electrophoretic sol-gel deposition of organically modified, sub-micron silica particles. The silica particles were modified with 3-aminopropyltriethoxysilane (APS) and vinyltriethoxysilane (VTES). Smooth and crack-free films ca. 15 m thick were obtained when APS modified silica particles were used for the cathodic electrophoretic deposition. Thick films with decreased open spaces among particles were obtained when silica particles modified with VTES were co-deposited with an organic polymer, polyethylene maleate.     

Mechanical properties and structural characteristics of PP/PP‐g‐SBR nanocomposites prepared by dynamical photografting

Poly(propylene) (PP)/PP grafted styrene‐butadiene rubber (PP‐g‐SBR) nanocomposite was prepared by blending PP with PP‐g‐SBR using dynamical photografting. The crystal morphological structure, thermal behavior, and mechanical properties of PP/PP‐g‐SBR nanocomposites have been studied by photoacoustic Fourier transform infrared spectroscopy (PAS‐FT‐IR), wide‐angle X‐ray diffraction (WAXD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and mechanical measurements. The data obtained from the mechanical measurements show that the PP‐g‐SBR as a modifier can considerably improve the mechanical properties of PP/PP‐g‐SBR nanocomposites, especially for the notched Izod impact strength (NIIS). The NIIS of the nanocomposite containing 2 wt% PP‐g‐SBR measured at 20°C is about 2.6 times that of the control sample. The results obtained from PAS‐FTIR, WAXD, SEM, and DSC measurements revealed the enhanced mechanism of impact strength of PP/PP‐g‐SBR nanocomposites as follows: (i) the β‐type crystal of PP formed and its content increased with increasing the photografting degree of PP‐g‐SBR; (ii) the size of PP‐g‐SBR phase in the PP/PP‐g‐SBR nanocomposites obviously reduced and thus the corresponding number of PP‐g‐SBR phase increased with increasing the photografting degree of PP‐g‐SBR. All the earlier changes on the crystal morphological structures are favorable for increasing the compatibility and enhancing the toughness of PP at low temperature. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis, characterization and thermal properties of novel PMDA-PAPD/silica hybrid network polymers

Novel PMDA-PAPD/silica hybrid polymers were synthesized by the sol-gel process. Fourier transform infrared spectroscopy and ²⁹Si nuclear magnetic resonance spectroscopy were used to characterize the structure of the hybrids, (condensed siloxane bonds designated as Q¹, Q², Q³, Q⁴, wth 3-aminopropyltriethoxysilane having mono-, di-, tri-, tetra-substituted siloxane bonds is designated as T¹, T² and T³). The results revealed that Q³, Q⁴ and T³ are the major microstructure elements in forming a network structure. The surface morphology, particle size, crystallinity and the thermal stability of the hybrids were investigated using Scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC). SEM and TEM revealed that the hybrids were nanocomposites. The XRD indicated that covalent bonding (Si-O-Si) between the organic and inorganic components enhanced miscibility. DSC and TGA results showed that these hybrid materials had excellent thermal stability. The heat capacities of some materials were reported for the temperature range 273 K and 363 K as no thermal anomaly was found in this temperature range.     

Preparation and characteristics of composites based on polypropylene and ultradispersed calcium carbonate

Feasibility studies directed at the parallel increase in the elastic modulus and impact toughness of polypropylene via introduction of ultradispersed CaCO₃ particles with sizes of 100 (Socal U1S2) and 60 nm (Socal 312V) have been performed. The effects of the content and sizes of CaCO₃ particles and the nature of a surfactant on the character of distribution of particles, the thermophysical characteristics of the polymer matrix, and the mechanical characteristics and heat resistance of the nanocomposites are analyzed. Microscopic studies reveal that nanoparticles show a tendency toward structuring. DSC studies have proved the nucleating action of ultrafine particles during the crystallization of PP. For the composites containing 15 vol % of Socal 312V CaCO₃ nanoparticles, the increase in the tensile elastic modulus achieves its maximum; depending on the nature of the surfactant, the reinforcing effect increases by 70-40%. As compared to the initial PP, the presence of ultrafine particles in the composites prevents a decrease in the storage modulus of PP with increasing temperature from 0 to 50°C; as a result, the reinforcing effect increases from 30-40% at temperatures below the glass transition temperature to 40–75% at 50°C. For the nanocomposites with U1S2 in the presence of Triton X-100 or fluorinated alcohol telomer, the impact toughness increases over the entire filler content interval; when the filler concentration is 15 vol %, the impact toughness of nanocomposites is higher than that of the initial PP by factors of 3 and 4.5, respectively. It has been found that nanocomposites containing 5 vol % CaCO₃ nanoparticles show the effect of thermal stabilization, which comes up to about 50°C.     

Effect of non-ionic surface active agents on TEOS-derived sols,gels and materials

The sol-gel process, starting from tetraethylorthosilicate precursor, is a suitable technique for the preparation of silica thin films. The use of specific organic additives, like non ionic surface-active agents, drastically modifies the gelation process and allows the preparation of microporous materials with a high microporous volume. The effects of additives on the sol, gel and material characteristics have been investigated by several methods such as ²⁹Si NMR, QELS, SAXS (for sols and gels), and N₂ adsorption, FESEM (for fired materials). It appears that the interactions of surface active agents with TEOS derived species limit condensation reactions and particle growing. A brittle gel structure is generated which leads to highly porous microporous silica after the elimination of organic chains by thermal treatment at 450°C. The material porous texture (specific surface area, pore size distribution and porous volume) can be varied especially by varying the surface active agent chain length and quantity. This kind of sol-gel system is suitable to prepare microporous silica membranes candidate for gas separation or catalytic reactor applications.     

Controlling morphology and particle size of hollow poly(styrene-divinylbenzene) microspheres fabricated by template-based method

Hollow poly(styrene–divinylbenzene) (P(S-DVB)) microspheres were fabricated via template-based method including synthesis of silica particles by sol-gel method, preparation of silica/P(S-DVB) particles by dispersion polymerization and chemical etching of silica cores by NaOH solution. TEM, FTIR and TG analyses confirmed that the hollow P(S-DVB) microspheres were successfully obtained. The morphology of hollow P(S-DVB) microspheres could be controlled by adjusting the amounts of DVB, AIBN and VTES, and the round-ball-like hollow P(S-DVB) microspheres were fabricated when the amount of DVB, AIBN and VTES was 30.0?wt%, 5.0?wt% and 30.0?vol% respectively. Both the size of silica particles and amount of monomers were regarded as the two key factors to control the particle size of the round-ball-like hollow P(S-DVB) microspheres.