Synthesis and cationic photopolymerization of new silicon‐containing oxetane monomers

The cationic photopolymerization of oxetane‐based systems containing silicon monomers was investigated. For this purpose, three new silicon‐containing oxetane monomers were synthesized through a simple and straightforward synthetic method. The silicon‐containing monomers were added to a typical oxetane resin, 3,3′‐[oxydi(methylene)]bis(3‐ethyloxetane), in concentrations of 1–5 wt %. They exploited a certain surface tension effect without affecting the rate of polymerization. Enrichment only on the air side was achieved, which induced hydrophobicity in the photocured films, depending on the monomer structure and concentration. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1415–1420, 2004     

High-flux,porous and homogeneous PVDF/cellulose microfiltration membranes

Low hydrophilicity of membranes is probably the biggest concern in membrane filtration since it increases the costs for water treatment. Conversely, application of hydrophilic biopolymers (such as cellulose) is limited because of its complex and crystalline structure. Enabling the wide use of the most common biopolymer in nature is crucial to improve the performance of water treatment, especially in terms of membrane sustainability. Here, we study the effect of cellulose dissolution in the synthesis of homogeneous PVDF/cellulose membranes. Although only partial dissolution was achieved for studied samples, adding cellulose to the membranes greatly improved their water flux. Besides, the porous structure obtained after partial solvent removal indicates the water flux (and consequently the pore size) may be tailored according to the membrane production method. Therefore, the homogeneous cellulose microfiltration membranes studied here may have potential for water treatment considering their high-water flux and low complexity to produce.

     

Thermal, rheological, and barrier properties of waterborne acrylic nanocomposite coatings based on boehmite or organo-modified montmorillonite

An organo-modified montmorillonite (Cloisite^®30B) or an unmodified boehmite (Disperal^®40) have been added to two acrylic latex dispersions (one of them UV-curable) for obtaining nanocomposite coatings. X-ray diffraction and transmission electron microscopy show a high degree of exfoliation in the nanocoatings based on montmorillonite, together with the deagglomeration of the micrometer-sized boehmite powder and the presence of single boehmite crystallites within the polymer matrix. Such morphologies are found to enhance the thermal and thermo-oxidative stability of the latexes and to significantly decrease their oxygen permeability, as well.     

Energetic potential of pyrolyzed biomass from different sources: a comparative study

Journal of Thermal Analysis and Calorimetry - The use of biomass has been a recent trend as a potential feedstock for char generation with improved energetic value. In this work, agricultural...     

Sol–gel treatments for enhancing flame retardancy and thermal stability of cotton fabrics: optimisation of the process and evaluation of the durability

Cotton fabrics have been treated by sol–gel processes in order to create a silica compact coating on the fibres to enhance their thermal stability and flame retardancy. The effect of process parameters such as silica precursor:water molar ratio and drying conditions (temperature and time) has been thoroughly investigated, aiming at optimization of target properties. Thermogravimetry and cone calorimetry have been respectively used to assess thermal stability and combustion behaviour of treated fabrics. Coating durability to different washing programmes has been evaluated as well.     

The stack loading and unloading problem

When piling a set of items in a single stack, one often does not pay attention to the order. Real-life experience suggests that, whenever a specific item is suddenly requested, we need to dig very deep into the stack to extract it.In this paper we investigate stack reordering strategies aiming at minimizing the number of pop and push operations. In particular we focus on three versions of the problem in which reordering can take place in different phases: when unloading the stack, when loading it or in both phases. We show that the first two variants can be solved in linear time, while for the third one we devise a dynamic programming method with quadratic complexity.     

Flammability and combustion properties of ammonium polyphosphate-/poly(acrylic acid)- based layer by layer architectures deposited on cotton,polyester and their blends

Layer by layer architectures consisting of four layer repetitive unit (QL) based on poly(diallydimethylammonium chloride)/poly(acrylic acid)/poly(diallydimethylammonium chloride)/ammonium polyphosphate have been deposited on cotton, polyester and their blends in order to promote the formation of an aromatic and stable carbonaceous structure (char) during combustion. The LbL-treated fabrics have been subjected to flammability (reaction to flame application) and combustion (reaction to different external heat fluxes) tests. The coatings were able to remarkably enhance the char formation of each substrate just after 1QL deposition; furthermore, 5 and 10QL assemblies have favoured the formation of intumescent-like structures with further improvement of the final residue. As a consequence, the treated fabrics have shown a strong reduction of the flammability (afterglow and incandescent melt dripping suppression) and combustion (reduced heat released). Infrared spectroscopy has pointed out the aromatic nature of the residues left after the combustion.     

Preparation and characterization of UV-cured acrylic nanocomposites based on modified organophilic montmorillonites

UV-cured nanocomposites have been prepared through the photopolymerization of the acrylic resin BEMA (Bisphenol A ethoxylate dimethacrylate) added with organophifilic montmorillonites. Two types of commercially available nanoclays namely Cloisite 30B and Cloisite Na⁺ were further modified with organic compatibilizers (dodecylsuccinic anhydride, octadecylamine, octadecanoic alcohol and octadecanoic acid) in order to increase their basal spacing and improve the dispersion in the acrylic matrix. The modification with the organic compatibilizers determined an increase of the interlayer distance, as revealed by XRD (X-Ray Diffraction) analysis. The different types of the modified nanoclays were then dispersed in BEMA monomer at 5% m/m concentration and UV-cured in order to prepare the nanocomposites. XRD measurements performed on the nanocomposites showed a slight increase of the interlayer distance indicating the formation of intercalated structures. The photopolymerization reaction was monitored through real-time FT-IR (Fourier Transform Infrared Spectroscopy) in order to check any influence of the nanofillers on the cure kinetics. The nanocomposites were investigated by DSC (Differential Scanning Calorimetry) and TG (Thermogravimetric) analyses and compared to the neat UV-cured resin. The presence of the nanofillers did not influence the glass transition temperature (T_g) of the acrylic resin; in addition an increase of the thermal stability in air of the nanocomposites was evidenced through TG analysis.     

Testing optimality for quadratic 0–1 unconstrained problems

This paper analyses a necessary and sufficient optimality condition for quadratic pseudo-Boolean unconstrained problems. It is proved that in general testing any necessary and sufficient optimality condition is a difficult task for anyNP-hard problem. An-optimality condition is derived together with an approximation scheme to test it.This work has been supported by the Progetto Finalizzato Trasporti 2, 93.01799.PF74.Professor Paolo Carraresi died unexpectedly on March 5, 1994. At the time of his death this paper had been completed. While undertaking the final revision, the other two authors were reminded just how much they were indebted to Professor Carraresi after many years of common work together.