Fernando Wypych

Nanocomposites: synthesis, structure, properties and new application opportunities

Nanocomposites, a high performance material exhibit unusual property combinations and unique design possibilities. With an estimated annual growth rate of about 25% and fastest demand to be in engineering plastics and elastomers, their potential is so striking that they are useful in several areas ranging from packaging to biomedical applications. In this unified overview the three types of matrix nanocomposites are presented underlining the need for these materials, their processing methods and some recent results on structure, properties and potential applications, perspectives including need for such materials in future space mission and other interesting applications together with market and safety aspects. Possible uses of natural materials such as clay based minerals, chrysotile and lignocellulosic fibers are highlighted. Being environmentally friendly, applications of nanocomposites offer new technology and business opportunities for several sectors of the aerospace, automotive, electronics and biotechnology industries.

Semiconductor-assisted photocatalytic degradation of reactive dyes in aqueous solution.

This work reports the semiconductor-assisted photochemical degradation of reactive dyes. In an oxygenated-UV-ZnO system almost total decolorization of Remazol Brilliant Blue R, Remazol Black B, Reactive Blue 221 and Reactive Blue 222 was observed in reaction times of about 60 min. Extending the photochemical treatment up to 120 min, mineralization higher than 80% for all the dyes was observed. During the same period, the residual acute toxicity was significantly reduced only for Remazol Black B. A systematic optimization study carried out by factorial design showed that for the reactive dyes tested, the ZnO semiconductor exhibits a better efficiency than that observed with anatase TiO2. A synergistic effect in the coupled TiO2-ZnO system was not observed.

Starch films reinforced with mineral clay

Abstract A mineral clay was used as filler in order to improve the mechanical properties of glycerol-plasticized Cara starch films. These were characterized by mechanical and dynamic mechanical analysis, X-ray diffraction (XRD), thermogravimetry, infrared spectroscopy, and scanning electron microscopy. Dynamic mechanical analyses showed that the composite films give rise to three relaxation processes, attributable to a transition of the glassy state of the glycerol-rich phase, to water loss including the interlayer water from the clay structure, and to the starch-rich phase. A film obtained with 30% in w/w of clay showed an increase of more than 70% in the Young modulus compared to non-reinforced plasticized starch. Both XRD and infrared spectroscopy showed that glycerol can be intercalated into the clay galleries and that there is a possible conformational change of starch in the plasticized starch/clay composite films. Clay exfoliation occurred in unplasticized starch/clay mixtures.

Semiconductor-assisted photodegradation of lignin, dye, and kraft effluent by Ag-doped ZnO

This work reports a preliminary study of semiconductor-assisted photochemical degradation of lignin, Remazol Brilliant Blue R and Kraft E1 paper effluent by using ZnO and Ag-doped ZnO photocatalysts. The doped semiconductor was prepared in the reaction media by photoreduction of silver nitrate. With the use of 100 mg of ZnO and 15 mg of Ag-ZnO, almost total decolorization of the dye and lignin samples in reaction times lower than 60 min were observed. Extending the photochemical reaction up to 120 min, the total organic carbon content (TOC) was reduced in 90%. For the paper effluent, a fast decolorization was obtained for relatively short reaction times. However, de TOC reduction was negligible (near of 10%) up to high reaction times (300 min). By using the Ag-ZnO photocatalyst, the toxicity of lignin and Kraft E1 effluent toward E. Coli was completely removed. For the dye, the formation of transient toxic species was observed.

Fractionation of Eucalyptus grandis chips by dilute acid-catalysed steam explosion

Steam explosion of Eucalyptus grandis has been carried out under various pretreatment conditions (200-210 degrees C, 2-5 min) after impregnation of the wood chips with 0.087 and 0.175% (w/w) H2SO4. This study, arranged as a 2(3) factorial design, indicated that pretreatment temperature is the most critical variable affecting the yield of steam-treated fractions. Pretreatment of 0.175% (w/w) H2SO4-impregnated chips at 210 degrees C for 2 min was the best condition for hemicellulose recovery (mostly as xylose) in the water soluble fraction, reaching almost 70% of the corresponding xylose theoretical yield. By contrast, lower pretreatment temperatures of 200 degrees C were enough to yield steam-treated substrates from which a 90% cellulose conversion was obtained in 48 h, using low enzyme loadings of a Celluclast 1.5 1 plus Novozym 188 mixture (Novo Nordisk). Release of water-soluble chromophores was monitored by UV spectroscopy and their concentration increased with pretreatment severity. The yield of alkali-soluble lignin increased at higher levels of acid impregnation and pretreatment temperatures. Thermoanalysis of these lignin fractions indicated a pattern of lignin fragmentation towards greater pretreatment severities but lignin condensation prevailed at the most drastic pretreatment conditions.

Layered polymer-kaolinite nanocomposites

Kaolinite (K) was reacted with liquid dimethyl sulfoxide (DMSO) producing K(DMSO)0.4. Highly ordered polymer/kaolinite materials were obtained by displacement of DMSO molecules in the K(DMSO)0.4 intercalate by polyethylene oxide (PEO) or bacterial polyhydroxybutyrate (PHB), both in the melt state at 130°C and 180°C, respectively. The hybrid nanocomposites obtained were characterized by powder X-ray diffractometry (PXRD), Fourier Transform Infrared spectrometry (FTIR) and thermal analysis (simultaneous TG/DSC). The obtained results are consistent with the total replacement of DMSO molecules by the macromolecular linear chains that lie flat building a monolayer of the polymer in the interlayer space of kaolinite. The stoichiometry of the compounds estimated from the TG/DSC measurements are: K(DMSO)0.40±0.02, K(PHB)0.82±0.02, K(PEO)3.40±0.02.

Dehydrated halloysite intercalated mechanochemically with urea: thermal behavior and structural aspects.

Urea has been intercalated mechanochemically into dehydrated halloysite and analyzed by X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance ultraviolet/visible spectroscopy (DRUV-VIS), thermal analysis (TGA/DTA), transmission electron microscopy (TEM), and electron paramagnetic resonance (EPR). The basal distance expands from 7.4 to 10.7 A and the interaction of urea to adjacent layers of halloysite through hydrogen bonds increases the structural order of the matrix. After heat treatment in air at different temperatures, decomposition products begin to appear starting from 100 degrees C. Although the basal distance remains constant up to 160 degrees C and collapses to the original value at 200 degrees C, urea and the decomposition products are still present in the sample. Starting from 125 degrees C, urea decomposition products reduce halloysite structural Fe3+ centers to Fe2+, as indicated by DRUV-VIS and EPR spectroscopy.

Synthesis and characterization of zeolite-encapsulated metalloporphyrins

Abstract Metalloporphyrins of FeIII and CuII were prepared inside the large pores of the zeolite NaY by a process of sequential introduction of components followed by assembly inside the void space of the zeolite. The appropriate process chosen for the porphyrin synthesis was using the propionic acid solvent for reaction between pyrrole and benzaldehyde and this solvent was not destructive for zeolite. The powder X-ray diffraction data confirmed that the crystallinity of the zeolite was maintained. The resulting materials were purified by Soxhlet extractor. The zeolite-included metalloporphyrins were identified for studies using UV-Vis, FTIR and EPR Spectroscopy, CA (chemical analysis), AAS (atomic absorption spectroscopy), TG/DSC, XRD, SEM and 13C-NMR techniques. The catalytic activity of these products was examined and the catalyst showed to be a promising catalytic system to aliphatic hydrocarbon oxidation reactions.

New multifunctional materials obtained by the intercalation of anionic dyes into layered zinc hydroxide nitrate followed by dispersion into poly(vinyl alcohol) (PVA)

Different anionic blue and orange dyes have been immobilized on a zinc hydroxide nitrate (Zn(5)(OH)(8)(NO(3))(2)nH(2)O--Zn-OH-NO(3)) by anion exchange with interlayer and/or outer surface nitrate ions of the layered matrix. Orange G (OG) was totally intercalated, orange II (OII) was partially intercalated, while Niagara blue 3B (NB) and Evans blue (EV) were only adsorbed at the outer surface. Several composite films of poly(vinyl alcohol)--PVA were prepared by casting through the dispersion of the hybrid material (Zn-OH-OG) into a PVA aqueous solution and evaporation of water in a vacuum oven. The obtained composite films were transparent, colored, and capable of absorbing UV radiation. Improved mechanical properties were also obtained in relation to the nonfilled PVA films. These results demonstrate the onset of a new range of potential applications for layered hydroxide salts in the preparation of polymer composite multifunctional materials.

Zn2Al layered double hydroxides intercalated and adsorbed with anionic blue dyes: a physico-chemical characterization.

Three different anionic blue organic dyes have been intercalated into the structure of Zn(2)Al layered double hydroxides, using the co-precipitation method at constant pH. Using the same synthetic procedure, Zn(2)Al-Cl has been prepared and used as an adsorptive phase to retain the blue dyes from an aqueous solution. All the organic/inorganic (O/I) hybrid LDH compounds were analyzed by X-ray powder diffraction (XRPD), thermal analysis (TG/DTA), elemental analysis, solid state (13)C nuclear magnetic resonance (CPMAS (13)C NMR), and Fourier transform infrared spectroscopy (FTIR). In the adsorption experiments, Gibbs free energy DeltaG values for the temperatures in a range between 10 and 40 degrees C were found to be negative, which indicates that the nature of adsorption is spontaneous and shows the affinity of LDH material towards the blue anionic dyes. Additionally a decrease in DeltaG values at higher temperature further indicates that this process is even more favorable at these conditions. The enthalpy DeltaH values were between physisorption and chemisorption, and it may be concluded that the process was a physical adsorption enhanced by a chemical effect, characterized by a combined adsorption/intercalation reaction, making these O/I assemblies reminiscent of the Maya blue.