Search

Photocatalytic oxidation processes (PCO) represent more and more promising technologies for air purification and the development of new solutions in pollution sensing and prevention by using adequate nanostructures with unique properties has gained more interest in the scientific community. The present work is meant to show the production, characterization and the photocatalytic performance of nanostructured membranes based on electrospun polyacrylonirile (PAN) scaffolds and graphene/titania based catalysts. Three different systems of photocatalyst were chosen in order to compare their photocatalytic properties: pristine TiO2, TiO2 plus a few-layers graphene and TiO2/reduced-graphene composite obtained by hydrothermal method from graphene oxide. Results of the photocatalytic performance on methanol gas-phase degradation, revealed a higher reaction rate of the graphene based photocatalysts wherein an effective charge transfer, enhanced by graphene, has been supposed to reduce the charge recombination increasing the photocatalytic activity of TiO2 nanoparticles. Moreover, it has been found that the performance of the nanostructured membranes can be restored by stripping with an inert gas several times and this property makes them a good candidate as active filter media.

A specific procedure is proposed for the univocal and fast identification of viscoelastic parameters of polymeric materials by the processing of experimental results from creep tests. Mechanical tests were developed on polymethylmethacrylate and polycarbonate samples according to different stress and temperature conditions. The creep stresses and the temperatures were defined to characterize the mechanical response within the standard domain of application of the specific polymeric materials. The experimental data were post-processed to provide the experimental relationship between creep modulus and time at the different temperatures. Such experimental relationship was interpreted by specific model formulations, which were developed starting from the standard theory of linear visco-elasticity. Elastic and viscous parameters were identified by the minimization of discrepancy between model and experimental results. The trend of constitutive parameters with temperature was finally evaluated.

Electrically conductive polypropylene nanocomposites containing multi-walled carbon nanotubes were produced by melt blending by dilution of a concentrate masterbatch containing 10 wt.% of filler. In order to promote polymer infiltration within primary agglomerates a ultra-low melt viscosity polypropylene grade has been used for masterbatch production. Moreover, three polypropylenes with different melt viscosities have been used for successive dilutions. Filler dispersion has been assessed by both indirect macroscale analyses and direct morphological investigations. Characterization showed percolation thresholds occurring for very low filler contents. During dilution, lower polymer viscosities lead to more effective residue agglomerates dispersion, hence better electrical properties.

This paper reports decomposition/pyrolysis studies of polyurethane (PU) rigid foams containing phosphinate, phosphonate or phosphate as flame retardant in order to study the effect of phosphorus oxidation state on their gas and/or solid phase action. The flame retardants analyzed were aluminium phosphinate (IPA), dimethylpropanphosphonate (DMPP), triethylphosphate (TEP) and ammonium polyphosphate (APP), which differ in oxidation state and/or decomposition temperature. Gases evolved during TGA analyses as well as solid residues have been studied by means of MS and FTIR. The results show that phosphorus flame retardants which significantly lose weight at temperatures lower than those of neat PU foams act in the gas phase irrespective of their valency: indeed, they are completely volatilized before polymer decomposition starts and thus no interaction between flame retardant and polymer can be expected. The effect of phosphorus oxidation state becomes important when flame retardant decomposition takes place in the same temperatures range as neat polymer. In this case, it seems that at lower P oxidation state (+1) a combined gas and solid phase action takes place while at higher P oxidation state (+5) only solid phase action was observed.

Polyurethane rigid nanocomposite foams were synthesized by in situ-polymerization using both pristine and organically modified layered silicates. The effect of synthesis conditions, in particular the effect of different dispersing techniques, on morphology and mechanical properties of polyurethane nanocomposite foams was studied. To promote dispersion, clays were dispersed either in polyols or isocyanate and were subjected to a well known dispersion method, like ultrasonication, but also to a new dispersion method, based on microwaving. The morphological characterization of the foams, carried on using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, proved that the technology based on microwave processing is able to provide very good silicates dispersion and requires very short application time to be effective. Further confirmations of the importance of the clay organo-modifier are still present. Mechanical characterization of foams show that clay interferes with H-bond formation and then the overall compressive performance of PU nanocomposite foams depends on the competition between the positive reinforcing effect of clay and the negative effect on H-bond formation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Synergy in flame retardancy of polyurethane foams between phosphorus-based flame retardant (aluminium phosphinate) and layered silicates has been investigated. We used pristine montmorillonite as well as ammonium modified clay (commercially available) and diphosphonium modified clay, which were synthesised by the intercalation of the quaternary diphosphonium salt according to a procedure reported here. The morphology of the foams was characterised through X-ray diffraction (XRD), while thermal properties were characterised by oxygen index test, cone calorimeter and thermogravimetric analysis (TGA). The morphological characterisation showed that pristine and diphosphonium modified clays are almost slightly intercalated, while ammonium modified one is very well dispersed. The results of thermal characterisation showed that in the presence of phosphinate enhancements of oxygen index, fire behaviour, measured by cone calorimeter, and thermal stability have been achieved. Phosphinate is therefore an efficient flame retardant for polyurethane foams and its flame retardancy action takes place in both condensed and gas phases. Pristine and ammonium modified layered silicate bring some enhancements of thermal stability while having no important effect in decreasing peak heat release rate (PHRR) and total heat evolved (THE) when used in conjunction with phosphinate; their main advantage is related to the enhancement of compactness of the char layer formed. Diphosphonium clay is instead effective in further improving the fire behaviour of the foams because of the flame retardancy action of phosphonium: both PHRR and THE were decreased. The analysis of cone calorimeter data showed that clays act through physical effect constituting a barrier at the surface which is effective in preventing or slowing the diffusion of volatiles and oxygen, while phosphinate and phosphonium are more effective owing to their combined action in both condensed and gas phases.

Nanocomposites of a charring polymer (like polyurethane foam) filled with aluminum phosphinate (AlPi) with or without melamine cyanurate (MelCy) have been prepared by microwave processing and their thermal stability and fire behavior have been studied. Results on the interaction between flame retardants and layered silicates were provided as well as detailed investigation of the char strength, which has been carried out using a suitably developed method based on dynamic-mechanic analysis. Generally, the thermo-oxidative stability in presence of layered silicates was higher than the counterparts even if an additive rather than synergic effect took place; however, in some cases the interaction between clays and phosphinate led to a significant decrease of weight residue. In nitrogen the residue amounts were about the same but a higher amount of phosphorus was retained in the solid phase in presence of clays. Cone calorimeter results showed that the use of phosphinates led to a decrease of the PHRR; further addition of clays did not reduce the PHRR owing to the worse quality of char layer as demonstrated by the char strength test. However, it has been shown that the partial substitution of aluminum phosphinate with melamine cyanurate gave improved results: the AlPi–MelCy filled foams showed similar pHRR and THE but lower TSR and higher char strength than AlPi filled foams. It was also confirmed that phosphinate acted by flame inhibition but its action was depressed by the use of nanoclays owing to their interaction.

The preparation and characterization of the diphosphonium montmorillonite (DP-MMT) obtained by the intercalation of the quaternary diphosphonium salt [MeOOCCH 2 (Ph) 2 PCH 2 CH 2 P(Ph) 2 CH 2 COOMe]Br 2 (DP-Br 2 ) is reported with the aim to use it in the preparation of polyurethane foam-nanocomposites and in the study of their thermal behavior. DP-MMT was prepared by reaction of Dellite HPS in hot water with DP in 1:1 CEC ratio. DP-MMT was characterized by X-ray diffraction which showed a basal ( d 001 ) spacing of 1.90 nm versus 1.25 nm of the unmodified starting Dellite. The basal spacing value is consistent with a bilayer arrangement of intercalated chains. DP-MMT was characterized by 31 P and 29 Si NMR in the solid state. TGA curves showed that at about 400 °C the weight loss in DP-MMT is ca. 18%. DP-MMT was then used in polyurethane rigid foam (PUR) synthesis (5 wt.%). DP-MMT and commercial ammonium-modified MMT (Cloisite ® 30B) as well as unmodified MMT (Dellite HPS) were used as filler for PUR foams, together with Al-hypophosphite. Thermal stabilities were compared.