Particle atomic layer deposition of alumina for sintering yttria-stabilized cubic zirconia

The addition of aluminum oxide (Al₂O₃) as a sintering aid to yttria-stabilized zirconia (YSZ) reduces the required densification temperature. Sintering aids are incorporated using a number of processes which can lead to ambiguity when determining the effect of the sintering aid on the densification mechanism. In this study, a novel method for sintering aid addition, Particle Atomic Layer Deposition (ALD), was used to deposit an amorphous Al₂O₃ thin film on YSZ particles. Transmission electron microscopy confirmed the deposition of conformal Al₂O₃ thin films on the surface of the YSZ particles. The addition of Al₂O₃ to YSZ reduced the temperature at which densification began by ~75°C, and 2.2 wt% Al₂O₃ addition resulted in a minimum activation energy for the intermediate stage of densification. This concentration is well in excess of the solubility limit of Al₂O₃ in YSZ, showing that Al₂O₃ does not enhance the densification of YSZ solely by dissolving into the YSZ lattice and activating volume diffusion. The addition of 0.7 wt% Al₂O₃ with one Particle ALD cycle enhanced the ionic conductivity of YSZ by 23% after sintering at 1350°C for 2 hours, demonstrating that dense parts with high oxygen ion conductivities can be produced after sintering at reduced temperatures. One Particle ALD cycle is a fast, easily scaled-up process that eliminates the use of solvents and has substantial cost/performance advantages over conventional processing.     

Reactions of cellulose and wood superficial hydroxy groups with organometallic compounds

Various lignocellulosic substrates, including microcrystalline cellulose, pinewood and hemp fibres, were treated with triethylaluminium and triethylboron in suspensions, in non‐swelling media. Chemical and spectroscopic analyses show that coupling surface reactions took place between one or two metal‐to‐carbon (Mt–C) bonds and the OH groups of the natural polymers. The remaining unreacted Mt–C bonds were exploited to graft numerous molecular structures derived from alcohols and amines. The occurrence of the second reaction was proved by Fourier‐transform infrared spectroscopy, elemental analyses, X‐ray photoelectron spectroscopy and contact angle measurements. Copyright © 2004 Society of Chemical Industry     

Alginate and alginate/hyaluronic acid membranes generated by electrospinning in wet conditions: Relationship between solution viscosity and spinnability

The methodology to create alginate and alginate/hyaluronic acid membranes, which involves wet conditions electrospinning, is presented in this paper. The wet conditions allow simultaneously to work in water solutions avoiding the toxic solvents and to obtain crosslinked alginate. An accurate rheological characterization of all solutions examined is performed. By optimizing the electrospinning parameters, it is possible to obtain alginate membranes with homogeneous nanofibers and a narrow diameter distribution (i.e., around 100 nm) as well as alginate/hyaluronic acid membranes characterized by a network of bimodal distribution of the dimensions, namely nanofibers with a diameter comparable to the ones of the alginate membrane, in which are blocked microfibers with a ribbon like appearance, as observed in the SEM images. In order to facilitate the electrospinning process, poly(ethylene oxide) is added to the solutions and then removed after membranes preparation, as demonstrated by the differential scanning calorimetry results, obtaining membranes made up only biopolymers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46390.     

Structural investigation of Poly(ethylene terephthalate)/Poly(trimethylene terephthalate) transesterificated blends

Wide-Angle X-ray Diffraction (WAXD) and Small-Angle X-ray Scattering analyses were carried out to evaluate the evolution of the crystalline and supermolecular structure of poly(ethylene terephthalate) (PET) blended with poly(trimethylene terephthalate) (PTT). The conditions adopted in preparing the PET/PTT 50/50 blend induce transesterification between the polyesters; these reactions produce a new molecular characteristics based on PET/PTT copolymer that exhibits its own WAXD profile. The PET/PTT 50/50 copolymers prepared by melt mixing of the homopolymers for increasing times evidence spherulitic morphology and an evolution of the crystalline structure in terms of crystallinity and crystal dimensions. The periodicity of the transesterificated samples is intermediate between the long periods observed for pure PET and pure PTT. For the PET/PTT 50/50 copolymers the value of periodicity and lamellar thickness increase with the increasing of the processing time.     

How to reach 100% selectivity in H2O2-based oxidation of 2,3,6-trimethylphenol to trimethyl-p-benzoquinone over Ti,Si-catalysts

A comprehensive study of structure/activity/selectivity relationships and mechanistic aspects of the oxidation of 2,3,6-trimethylphenol (TMP) with aqueous H₂O₂ over a wide variety of titanium-silicate catalysts allowed us to infer requirements to an optimal catalyst and optimal reaction conditions for this reaction and to produce 2,3,5-trimethyl-1,4-benzoquinone (TMBQ, Vitamin E precursor) with nearly 100% selectivity at 100% substrate conversion. The main by-products in the TMP oxidation are C–C and C–O dimers, formed by coupling of intermediate phenoxyl radicals. The formation of TMBQ is favoured by (1) a poor coordinating solvent (MeCN), (2) elevated temperature (80 °C), (3) low TMP concentration (not higher than 0.1 M), (4) high H₂O₂/TMP molar ratio (ca. 3.5), and (5) low TMP/Ti ratio (<10–20). The crucial factors which determine the selectivity of Ti,Si-catalysts in TMP oxidation to TMBQ are mesoporosity and an optimal surface concentration (ca. 0.7–1.0 Ti atoms/nm²) of accessible highly dispersed, probably, dimeric Ti(IV) species. The catalysts prepared by a simple, affordable and cheap synthesis methodology via grafting titanium(IV) precursors onto the surface of commercial mesoporous silica completely fulfil these requirements and thus can be viewed as promising catalysts for environmentally benign TMBQ production.     

Poly(ether ether ketone) solutions suitable for microfiltration membrane preparation

Poly(ether ether ketone) shows high stability against chemical and physical agents but is poorly soluble in most common solvents. We tested new solvents to obtain concentrated solutions that we used to prepare microfiltration membranes by the phase‐inversion technique. The prepared membranes were tested by the filtration of oily emulsions, and their structure was studied with scanning electron microscopy. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2550–2555, 2001     

Titanium–Silica Catalysts for the Production of Fully Epoxidised Fatty Acid Methyl Esters

Grafted titanium-containing mesoporous silica catalysts were used in the selective epoxidation of C-18 unsaturated fatty acid methyl esters (FAMEs). High yields in mono- and diepoxide derivatives were obtained under acid-free reaction conditions with TBHP as oxidant. Ti-MCM-41 showed the best performance in terms of activity over the three FAMEs. Easy separation of the desired products and recycling of the catalyst were demonstrated.     

Surface modification of silica: 1. Thermodynamic aspects and effect on elastomer reinforcement

A thorough investigation of the interactions between silica and elastomers was conducted with the specific aim of understanding how the degree of modification with bis-triethoxysilylpropyltetrasulfane (TESPT) influences the surface energy of the filler and the tensile properties of technical compounds. The results of a thermodynamic study carried out by Inverse Gas Chromatography (IGC) at infinite dilution on silica modified with different amounts of TESPT indicate that from 6 to 8 wt% of grafted TESPT the surface activity of silica is considerably reduced and prevents particle fillers from interacting with each others. Tensile measurements at very low and high deformations carried out on vulcanised compounds loaded with silica, either unmodified or modified with different amounts of TESPT, confirm our thermodynamic predictions and further support the role of TESPT in promoting interactions between filler and elastomer, in achieving better dispersions and in improving mechanical properties.