Ti-Si mixed oxides prepared by polymer in situ sol-gel chemistry with the aid of CO2

A method to prepare titania-silica binary oxides is proposed in this work. In this route, inorganic precursors tetraethyl orthosilicate (TEOS) and titanium isopropoxide (TIP) were simultaneously or sequentially impregnated into a polypropylene (PP) matrix using supercritical carbon dioxide as a swelling agent and carrier. Hydrolysis and condensation reaction of the precursors confined in a polymer network were induced by treating the composites in 1 mol.dm(-3) (1 M) HCl. Then the PP matrix was decomposed at higher temperature, and titania-silica binary oxides were obtained. The mixed oxides were characterized by X-ray diffraction and Raman, FTIR, and X-ray photoelectron spectroscopy. It was demonstrated that the structure of the oxides depended strongly on the procedure to impregnate the precursors. The simultaneous method, in which the TEOS and TIP were simultaneously impregnated into a PP matrix, resulted in mixed oxides with highly dispersed titanium oxide species in the SiO2 matrix, while the sequential method produced the mixed oxide with separate SiO2 and TiO2 phases which were connected by Ti-O-Si bands at the interface. The method described in this work provides a new route to control the texture of TiO2-SiO2 mixed oxide simply by the impregnation sequence.     

Deformation of disentangled polypropylene crystalline grains into nanofibers

It was shown that a solid‐state deformation of polypropylene (PP) being in the form of partially disentangled powder is possible by blending with another molten polymer. During mixing of disentangled polypropylene powder with polystyrene at the temperature below melting of polypropylene crystals the shear forces deform powder grains into nanofibers. All disentangled powder particles larger than 0.7 µm underwent deformation into nanofibers having the mean thickness between 100 and 200 nm. Polypropylene nanofibers got entangled during blending and form a network within polystyrene matrix, reinforcing it. Network of entangled nanofibers can be further deformed with pronounced strain hardening and strength reaching 70 MPa at 135 °C. Blending resulted in generation of PP nanofibers and formation of PP nanofibers entangled network, thus formation of “all‐polymer nanocomposites” in one step compounding. The crucial feature for ultra‐deformation of PP grains by shearing during mixing is disentanglement of macromolecules. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1983–1994     

Synthesis of polymer–inorganic patchy microcapsules with tunable patches

We introduce a facile and versatile approach for the formation of ball-like polymer–inorganic patchy microcapsules with a tunable shell by combining sol–gel chemistry of silica precursor and phase separation between the polymer and the precursor. Firstly, chloroform-in-water emulsion droplets containing poly(methyl methacrylate) (PMMA), silica precursor [tetraethyl orthosilicate (TEOS)] and co-surfactant sodium dioctyl sulfosuccinate (Aerosol OT or AOT) were prepared by shaking the mixture by hand. Due to the added AOT, water molecules diffuse into the chloroform droplets, and the tiny water droplets would coalesce gradually, triggering the formation of double emulsion droplets. Upon further solvent evaporation, the concentration of the polymer and the silica precursor in the oil shell of the double emulsions increases, leading to the phase separation between the polymer and the precursors (and partially formed silica through the hydrolysis and condensation of TEOS). Because of the confined geometry of the oil shell in the double emulsions, polymeric disc-like structures, stabilized by AOT, were dispersed in the silica precursors. Meanwhile, the silica precursor hydrolyzed and condensed when brought in contact with the aqueous solution, ultimately leading to the formation of a mineralized shell around the polymer domains and the hybrid patchy microcapsules. Effect of synthesis conditions, such as the amount of TEOS, AOT, and PMMA used, the pH value, and solvent evaporation rate on interfacial behavior of the solvent/water; and the morphology of the patchy microcapsules were investigated. Patchy microcapsules with tunable patch size and shape can be generated through tailoring the experimental parameters. Our study indicates that the hybrid patchy microcapsules can be formed by taking advantage of the sol–gel chemistry and the phase separation process, and the underlying generality of the synthesis procedure allows for a variety of applications, including drug storage, coatings, delivery, catalysis, and smart building blocks in self-assembling systems.     

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.     

Influence of a non-polar medium (alkane and molten polypropylene) on the titanium n-butoxide hydrolysis-condensation reactions

Study of hydrolysis-condensation reactions of titanium n-butoxide precursor into an unusual medium and non-classical conditions was carried out. Kinetic data were reached in a temperature range of 130–250°C from FTIR, TGA–GC–MS and rheological techniques. These results were obtained into an alkane dispersing medium, (Squalane: 2,6,10,15,19,23-hexamethyltetracosane), and compared to the ones determined from the hydrolysis-condensation reactions of the titanium dioxide precursor carried in molten polypropylene (PP) during extrusion process. The transposition of these knowledge to the in situ synthesis of titanium dioxide in molten PP matrix by reactive extrusion lead to the formation of a fine dispersion of few nanometer diameter (~5 nm) of TiO₂ particles. Finally, the viscoelastic behaviour of the nanocomposite has been strongly altered in the terminal relaxation zone as permanent secondary plateau (solid-like behavior), attributed to some fractal arrangement of the inorganic domains was observed.     

Synthesis and characterization of UV‐curable phosphorus containing hybrid materials prepared by sol–gel technique

In this study, a series of ultraviolet (UV)‐curable organic–inorganic hybrid coating materials containing phosphorus were prepared by sol–gel approach from acrylate end‐capped urethane resin, acrylated phenyl phosphine oxide oligomer (APPO), and inorganic precursors. TEOS and MAPTMS were used to obtain the silica network and Ti:acac complex was employed for the formation of the titania network in the hybrid coating systems. Coating performance of the hybrid coating materials applied on aluminum substrates was determined by the analysis techniques, such as hardness, gloss, impact strength, cross‐cut adhesion, taber abrasion resistance, which were accepted by international organization. Also, stress–strain test of the hybrids was carried out on the free films. These measurements showed that all the properties of the hybrids were enhanced effectively by gradual increase in sol–gel precursors and APPO oligomer content. The thermal behavior of the hybrid coatings was investigated by thermogravimetric analysis (TGA) analysis. The flame retardancy of the hybrid materials was examined by the limiting oxygen index (LOI); the LOI values of pure organic coating (BF) increased from 31 to 44 for the hybrid materials containing phosphorus (BF‐P:40/Si:10). The data from thermal analysis and LOI showed that the hybrid coating materials containing phosphorus have higher thermal stability and flame resistance properties than the organic polymer. Besides that, it was found that the double bond conversion values for the hybrid mixtures were adequate in order to form an organic matrix. The polycondensation reactions of TEOS and MAPTMS compounds were also investigated by ²⁹Si‐NMR spectroscopy. SEM studies of the hybrid coatings showed that silica/titania particles were homogenously dispersed through the organic matrix. In addition, it was determined that the hybrid material containing phosphorus and silica showed fibrillar structure. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation of mesoporous submicrometer silica capsules via an interfacial sol-gel process in inverse miniemulsion

Mesoporous silica capsules with submicrometer sizes were successfully prepared via the interfacial hydrolysis and condensation reactions of tetraethoxysilane (TEOS) in inverse miniemulsion by using hydrophilic liquid droplets as template. The inverse miniemulsions containing pH-controlled hydrophilic droplets were first prepared via sonication by using poly(ethylene-co-butylene)-b-poly(ethylene oxide) (P(E/B)-PEO) or SPAN 80 as surfactant. TEOS was directly introduced to the continuous phase of an inverse miniemulsion. The silica shell was formed by the deposition of silica on the surface of droplets. The formation of capsule morphology was confirmed by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The mesoporous structure was verified by nitrogen sorption measurements. The specific surface area could be tuned by the variation of the amount of cetyltrimethylammonium bromide (CTAB) and TEOS, and the pore size by the amount of CTAB. The influences of synthetic parameters on the particle size and morphology were investigated in terms of the amount of CTAB, pH value in the droplets, TEOS amount, surfactant amount, and type of solvent with low polarity. A formation mechanism of silica capsules was proposed.     

Phosphorylated silica/polyamide 6 nanocomposites synthesis by in situ sol–gel method in molten conditions: Impact on the fire-retardancy

Polyamide 6 (PA6)/phosphorylated silica nanocomposites were synthesized during PA6 extrusion through in situ formation of the inorganic phase without solvent. This synthesis is based on the hydrolysis-condensation reactions of diethylphosphatoethyltriethoxysilane (SiP) as a functional inorganic precursor in combination with or without tetraethoxysilane (TEOS) dispersed in the molten PA6. This synthesis is carried out during PA 6 matrix extrusion that means at high temperature and under shear. The characterization of the in situ synthesized PA6/phosphorylated silica nanocomposites by solid ²⁹Si Nuclear Magnetic Resonance (NMR), Small Angle X-ray Scattering (SAXS) and Transmission Electron Microscopy (TEM) coupled with Energy Dispersive X-ray spectroscopy (EDX) demonstrated the possibility to directly create in less than 5 min at 220 °C a phosphorylated silica uniformly dispersed in the PA6, i.e. in the form of well dispersed particles or aggregates of sub-micron range. The influence of silicon and phosphorus on the thermal and fire retardant behaviour was investigated by thermogravimetric analysis (TGA), cone calorimeter and UL94 tests. The fire retardant behaviour was modified with a formation of a char and a peak heat release rate (PHRR) decrease by more than 50% for the SiP based nanocomposite compared to the pure PA6.     

High-pressure crystallization of isotactic polypropylene droplets

Dispersions of isotactic polypropylene (PP) particles in polystyrene (PS) were produced by interfacially driven breakup of nanolayers in multilayered systems that were fabricated by means of layer-multiplying coextrusion. The droplet size was controlled by the individual PP layer thickness ranging from 12 to 200?nm. In addition, PP was melt blended with PS to produce PP droplets larger than those formed by breakup of nanolayers. The dispersions of PP particles in the PS matrix were melted and annealed under high pressure of 200?MPa. Only the largest PP droplets, with average sizes of 170?μm, crystallized predominantly in the γ form. In the 42-μm droplets obtained by breakup of 200?nm layers, a minor content of the γ form was found whereas the smaller droplets obtained by breakup of the thinner nanolayers contained the α form and/or the mesophase. The results showed that the γ phase formed only in the droplets sufficiently large to contain the most active heterogeneities nucleating PP crystallization under atmospheric pressure. It is concluded that the presence of nucleating heterogeneities is necessary for crystallization of PP in the γ form under high pressure.     

共溶剂对超临界CO_2注入技术制备聚丙烯/SiO_2纳米复合材料的影响(英文)

采用超临界CO2注入技术制备聚合物-无机纳米粒子复合材料,以乙醇作为共溶剂,在超临界CO2中将正硅酸乙酯(TEOS)注入到聚丙烯(PP)中,重点研究共溶剂乙醇对TEOS在PP中注入率的影响.实验结果表明注入率随着共溶剂加入先增加后减小.同时研究了在共溶剂的存在下其他实验条件对注入率的影响.并采用卢瑟福背散射能谱法(RBS)分析了聚丙烯/SiO2纳米复合材料的注入元素深度分布,发现Si元素在PP中的浓度分布不均匀,随着深度的增加而减小.     

共溶剂对超临界CO2注入技术制备聚丙烯/SiO2纳米复合材料的影响

采用超临界CO2注入技术制备聚合物-无机纳米粒子复合材料, 以乙醇作为共溶剂, 在超临界CO2中将正硅酸乙酯(TEOS)注入到聚丙烯(PP)中, 重点研究共溶剂乙醇对TEOS在PP中注入率的影响. 实验结果表明注入率随着共溶剂加入先增加后减小. 同时研究了在共溶剂的存在下其他实验条件对注入率的影响. 并采用卢瑟福背散射能谱法(RBS)分析了聚丙烯/SiO2纳米复合材料的注入元素深度分布, 发现Si元素在PP中的浓度分布不均匀, 随着深度的增加而减小.     

Fractionated crystallization and morphology of PP/PS blends in the presence of silica nanoparticles with different surface chemistries

The fractionated crystallization behavior of polypropylene (PP) droplets in its 20/80 blends with polystyrene (PS) in the presence of hydrophilic or hydrophobic fumed silica nanoparticles was studied by using differential scanning calorimetry, scanning electron microscopy, and transmission electron microscopy. It was found that the fractionated crystallization of PP droplets in the PS matrix was promoted by adding a low content of hydrophobic or hydrophilic nanoparticles due to their morphological refinement effect. However, discrepancies in the fractionated crystallization behavior of PP droplets occurred as the nanoparticle content increased. The crystallization became dominated by the heterogeneous nucleation effect of high content of hydrophilic nanoparticles, which possibly migrated into PP droplets during mixing and significantly suppressed their fractionated crystallization. In contrast, the morphological refinement effect still played a dominated role in promoting the fractionated crystallization of PP droplets in PP/PS blends filled with higher content hydrophobic nanoparticles as a result of the efficiently morphological refinement effect.     

Synthesis and characterisation of elastomeric composites prepared from epoxidised styrene butadiene rubber, 3-aminopropyltriethoxysilane and tetraethoxysilane

Hybrid composite materials were obtained by the reaction of epoxidised styrene butadiene rubber with 3-aminopropyltriethoxysilane, followed by in situ hydrolysis and polycondensation of tetraethoxysilane (TEOS). The hybrid films were characterised by thermogravimetric analysis, differential scanning calorimetry, swelling and stress–strain measurements, scanning electron microscopy and infrared spectrometry. Non-solubility of the films in tetrahydrofuran indicated the formation of a network, the microstructure of which varied according to the concentrations of the inorganic precursors employed. The thermal stabilities of the films were similar to that of rubber, and the mechanical stress increased considerably with the amount of silica incorporated. The most transparent films were those prepared with the lowest concentrations of inorganic precursors, whilst those obtained using larger amounts of TEOS showed distinct microscopic phases. The protocol described represents a simple method by which to bind inorganic precursors to rubbers.     

Behaviour of phenol red pH-sensors in the presence of different surfactants using the sol-gel process

Phenol red was immobilised into a polysiloxane matrix using a sol-gel process to form pH optical sensors. The sol-gel was obtained by hydrolysis of tetraethoxysilane (TEOS) in the presence of phenol red (PR) and the appropriate surfactant. Different surfactants, namely cetyltrimethylammonium bromide (CTAB), dodecyldimetyl amino-oxide (GLA) and Triton X-100 (TX-100), were employed. Interestingly, the use of surfactants significantly improved the mesostructure of the silica and increased the porosity of the system. The two response pH ranges were shifted to pH 0.0–3.0 and pH 10.5–1.5M [OH^?] compared with those of the free PR (pH 0.0–3.0 and pH 6.5–9.5). It is found that the pH response and the pKa shift of the phenol red were dependent, not only on the silica matrix but also on the ionic properties of surfactants. In the case of ionic surfactants such as CTAB or GLA, there was further shift to more acidic and more basic pH, whereas in the case of non-ionic surfactants such as TX-100 no significant change of the pH curve was observed.     

Effects of pH on mechanical and morphological studies of silica filled polyvinyl chloride-50% epoxidized natural rubber (PVC-ENR50) nanocomposite

Effects of pH on mechanical properties as well as morphological studies of sol–gel derived in situ silica in polyvinyl chloride-50% epoxidized natural rubber (PVC-ENR50) nanocomposites are reported. In particular, a range of acid concentrations was investigated. These nanocomposites were prepared by solution casting technique and tetraethoxysilane (TEOS) was used as the silica precursor. The prepared nanocomposites were characterized using tensile test, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The tensile test indicated that the highest mechanical strength was at 30% TEOS added for the nanocomposite prepared at pH 2.0. At pH 1.0 and 1.5 the maximum tensile strength reading was at 20% TEOS added with value of 24.3 and 24.5 MPa, respectively. SEM and TEM revealed the dispersion of silica particles in the polymer matrix. For nanocomposites prepared at pH 1.0 and 1.5, the silica particles were finely dispersed with the average size of 60 nm until 20% TEOS added. Meanwhile for nanocomposite prepared at pH 2.0, silica particles were homogenously distributed in the polymer matrix with average diameter of 30 nm until 30% TEOS and agglomerated after 30% TEOS loading.     

Preparation of silica capsules via an acid-catalyzed sol–gel process in inverse miniemulsions

Silica capsules were prepared via a sol–gel process using tetraethyl orthosilicate (TEOS) in inverse miniemulsions under highly acidic conditions (pH?<?2). Formation of silica capsules under acidic conditions proceeded via internal phase separation of silica species in the droplets. This mechanism is different from the well-known interfacial reaction mechanism for most syntheses of silica capsules. The driving force for the formation of capsules was the interaction between silica species and cetyltrimethylammonium bromide (CTAB) as well as between silica species and the hydrophilic block of the block copolymer surfactant, poly(ethylene-co-butylene)-b-poly(ethylene oxide) (P(E/B)-PEO). The effects of synthetic parameters on the particle morphology and size were systematically investigated in terms of the reaction time, amount of TEOS, CTAB, P(E/B)-PEO, and hydrochloric acid concentration, as well as addition of ethanol.     

Morphology and viscoelasticity of PP/TiO2 nanocomposites prepared by in situ sol–gel method

PP/TiO₂ nanocomposites were prepared from an original method based on the hydrolysis‐condensation (sol–gel method) reactions of titanium alkoxide inorganic precursor premixed with polypropylene (PP) under molten conditions. Nanocomposites with a mean diameter of primary particles lower than 5 nm were then prepared. The TiO₂ particle dispersion in the PP matrix was characterized over a wide length scale from the combination of small angle X‐ray scattering, transmission electron microscopy, and linear viscoelasticty of molten nanocomposites. As a result, a fractal structure of these particles was highlighted at the highest concentration (φ_r ≥ 0.014) with a characteristic aggregation size d_aggr ≈ 130 nm. The relationships between fractal structure and linear viscoelastic have been discussed from the main works of the literature on the reinforcement of nanocomposites. The drastic alteration of the terminal relaxation zone (solid‐like behavior) is correlated to the formation of an aggregate‐particle network. The study of the nonlinear viscoelastic behavior (Payne effect) agrees qualitatively with this reinforcement mechanism. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1213–1222, 2010     

Formation and transformation of smectic polypropylene nanodroplets

A dispersion of isotactic polypropylene (PP) nanoparticles was produced by interfacially‐driven breakup of PP nanolayers. Layer‐multiplying coextrusion was used to fabricate an assembly of 257 alternating PP nanolayers about 12 nm thick sandwiched between thicker polystyrene (PS) layers. Characterization by thermal analysis and wide‐angle X‐ray diffraction (WAXD) confirmed that PP crystallized primarily in the smectic form when confined as nanolayers. When the layered assembly was heated into the melt, the PP nanolayers broke up to form a dispersion of PP droplets in a PS matrix. After solidification, particle size analysis revealed that 90% of the PP was present as 30 nm nanoparticles. The particles were small enough and numerous enough that most did not contain a primary nucleus. When cooled from melt at 10 °C min^?1, the droplets crystallized by homogeneous nucleation at 40 °C. The droplets were found to be in the smectic form by WAXD. Because crystallization occurred below the temperature of the smectic to α‐form transformation, the intermediate smectic form was stable and did not convert to the α‐form until heated above 70 °C. This result provided direct evidence for an intermediate smectic phase in the process whereby homogeneous nucleation leads to α‐form crystals in confined nanoparticles. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1795–1803, 2006     

Synthesis,Characterization and Properties of (Vinyl Triethoxy Silane-grafted PP)/Silica Nanocomposites

A new route has been developed to produce PP/silica nanocomposites starting from porous PP reactor powder and making use of sol-gel chemistry. Silica-like, nano-sized particles were prepared in the pores of the PP reactor powder with a controlled degree of adhesion between PP and silica. Magic-angle spinning (MAS) ²⁹Si NMR spectra showed that the chemical building blocks of the silica-like clusters are of Q³ and Q⁴-type. For (vinyl triethoxy silane (VTES)-grafted PP)/silica nanocomposites, VTES was grafted via solid-state modification (SSM) in porous PP particles. Subsequently, silica particles were prepared by sol-gel technology in the VTES-grafted PP. MAS ²⁹Si NMR and FT-IR spectroscopy showed that the grafted VTES becomes part of the in-situ formed silica particles. The study on the mechanical properties of (VTES-grafted PP)/silica nanocomposites showed that the silica particles improved the impact toughness of PP by a factor of 2, when there is no chemical interaction between the particles and the matrix, while for (VTES-grafted PP)/silica nanocomposites the impact toughness decreased. This indicates that chemical bonding between the filler particles and the PP-matrix results in brittle failure and supports the hypothesis that debonding is necessary for improving the impact toughness of PP with inorganic fillers.     

Stratified morphology of a polypropylene/elastomer blend following channel flow

A thermoplastic olefin blend consisting of isotactic polypropylene (PP) and an ethylene‐butene copolymer (EBR) impact modifier (25 wt % EBR) was subjected to a short, high‐shear pulse within the flow channel of a pressure‐driven microextruder following low‐shear channel filling from a reservoir of the melt. The resulting morphology was examined by laser scanning confocal fluorescence microscopy (LSCFM), with contrast provided by a fluorescent tracer in the EBR minor phase. Shear experiments were performed under isothermal conditions with a known wall shear stress for a specified duration, providing a well‐defined thermal and flow history. Low‐shear channel filling produces small droplets across the central region of the channel and large droplets, consistent with steady‐state shear, in the regions near the channel walls. After cooling the molten blend to a crystallization temperature of 153 °C, a brief interval (5 s ～ 1/2000 of the quiescent crystallization time) of high shear (wall shear stress: 0.1 MPa) induces rapid, highly oriented crystallization and a stratified morphology. Ex situ LSCFM reveals a “skin” at the channel walls (～70 μm) in which greatly elongated fiberlike droplets, oriented along the flow direction, are embedded in highly oriented crystalline PP. Further from the walls but directly beside the skin layers are surprising zones in which EBR domains show no deformation or orientation. Several zones of intermediate deformation and orientation at an angle to the flow direction are located closer to the center of the channel. At the center of the channel, EBR droplets are spherical, as expected for channel flow. The various strata are explained by the interplay of droplet deformation, breakup, and coalescence with the shear‐induced crystallization kinetics of the matrix. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2842–2859, 2002