1,720,996 research outputs found
Absorption of n-butyl acetate from tannery air emissions by waste vegetable oil/water emulsions
Full text linkTanning industries emit a huge quantity of Volatile Organic Compounds (VOCs), including hydrophilic and
hydrophobic solvents. In this study, vegetable oil/water emulsions with 2 and 5 vol% of corn oil (O) or waste
cooking oil (WCO) were prepared. Their potential as absorbents of n-butyl acetate (BA), in place of water, was
investigated to increase the efficiency of tannery wet scrubbers. BA was selected as a representative component
of hydrophobic VOC emissions derived from leather finishing processes. Static and dynamic absorption tests were
performed with a BA concentration of 500 ppmv (2.6 g/m3
) and a flowrate of 3.0 L/min to evaluate Henry’s law
constant, absorption efficiency, absorption capacity, and saturation time of the various investigated absorbents.
The feasibility of the absorbent regeneration was also studied by hot stripping with nitrogen. The results showed
that Henry’s constant of BA in oil/surfactant/water or oil/water emulsions (5 vol% oil), regardless of the oil
used, were significantly lower than those in water (3.6 versus 15.9 atm), and BA absorption capacity (0.84 g/L)
was four times higher than the value in water. The presence of the surfactant (0.2–0.8 vol%) contributed to
improving the oil/water emulsions stability without having a significant effect on BA absorption capacity. Almost
complete BA desorption from the saturated emulsions was obtained by flowing hot N2 at 80◦C, demonstrating the
absorbent regeneration’s feasibility followed by recovery and reuse. Therefore, the oil/water emulsions containing 5 vol% of WCO are efficient and sustainable absorbents of BA, with potential use in VOC emission treatment systems
Effect of Nanoadditives on Bitumen Aging Resistance: A Critical Review
Full text linkStarting from the eighties, the use of nanoadditives registered an increasing attention in the scientific and patent literature, especially for the case of polymeric nanocomposites. In the last decade, this involved bituminous materials, modified either with nanosized fillers or with polymeric nanocomposites. One of the expected benefits is an increased resistance of the binder to aging. After a short introduction underlining the uncertainties and risks of artefacts in aging tests, a review is given, focusing on the antiaging properties of layered silicates, which are by far the most important nanoadditives for bitumens. Together with layered silicates, other materials such as nanohydrated lime, nanosilica, and layered double hydroxides are mentioned. Preparation and characterization of the binary bitumen/layered silicate and ternary bitumen/layered silicate/polymer systems are described in order to individuate the aspects that influence the antiaging effect. Even if the available literature is quite abundant and unanimously confirms that nanoadditives may improve bitumen durability, there is a lack of studies clarifying the involved mechanisms. As it is for conventional fillers, it seems to be a combination of physical and chemical interactions. Nanoadditives with different chemistries, porosities, and interlayer spacings differently absorb the polar components from the bitumen, thus affecting their predisposition to oxidative aging
Azidated Ether-Butadiene-Ether Block Copolymers as Binders for Solid Propellants
Full text linkPolymeric binders for solid propellants are usually based on hydroxyl-terminated polybutadiene (HTPB), which does not contribute to the overall energy output. Azidic polyethers represent an interesting alternative but may have poorer mechanical properties. Polybutadiene–polyether copolymers may combine the advantages of both. Four different ether-butadiene-ether triblock copolymers were prepared and azidated starting from halogenated and/or tosylated monomers using HTPB as initiator. The presence of the butadiene block complicates the azidation step and reduces the storage stability of the azidic polymer. Nevertheless, the procedure allows modifying the binder properties by varying the type and lengths of the energetic blocks
A revised relationship between molecular weight and reduced angular frequency in δ-method applied to unmodified petroleum bitumens
No full textThe δ-method has been developed to estimate molecular weight distributions of bitumens from phase-angle master curves. The method uses a correlation between the cross-over frequency(ωC) and the molecular weight
(MW) that was developed from average MW measured by vapour pressure
osmometry. This study proposes a revised correlation whose parameters
have been calculated from Gel Permeation Chromatography (GPC), which
can be conducted at a low level of dilution preserving the interactions in the
bitumen bulk. Furthermore, data from the GPC allow the optimisation of the
parameters considering the entire MW distribution (MWD), thus improving
the predictive capability of the method. Three unmodified petroleum bitumens at different levels of ageing and three rheological models were used
in the optimisation. Two groups of parameters were identified; one for hard
(e.g. Pen 35-50) and another one for soft-medium bitumens (e.g. Pen 50–70
or Pen 70-100). The apparent-MWDs (A-MWDs) calculated with the new
parameters show improved correlation with the respective distributions
and average molecular weight from GPC
Limiting oxygen index reduction in bitumen modified with nanoclays
No full textOrgano-modified nanoclays may improve the fire resistance of polymers and bitumen. However, in some cases the nanoclay determines a reduction in the limiting oxygen index (LOI). In polymers, this effect is attributed to an increase of viscosity that limits the dripping of the molten samples during combustion. However, in the case of bitumen this explanation is not sufficient because the reduction is not always associated to high viscosities. In contrast, the mass losses recorded by thermogravimetry in well-defined temperature regions seems to correlate with LOI. Both viscosity and decomposition kinetic of the binders suggest that the nanoclays establish a high degree of interaction with the bitumen, thus determining a significant re-arrangement of its colloidal structure
Glycidyl Azide-butadiene Block Copolymers: Synthesis from the Homopolymers and a Chain Extender
No full textGlycidyl azide polymer (GAP) is an “energetic” alternative
to hydroxyl-terminated polybutadiene (HTPB), but
has poorer mechanical properties. Since HTPB-GAP mechanical
blends are markedly biphasic, the use of block copolymers
may be the solution to join the advantages of
both. The copolymers were synthesized from the homopolymers
by using two chain extenders: hexamethylene diisocyanate
(HDI) and adipoyl chloride (AdCl). Both reagents
gave homogeneous and stable polymeric mixtures, but
with HDI there are risks of gelation during reaction. Therefore,
the product obtained with AdCl is the best candidate
to be used as binder or as compatibilizer in GAP-HTPB mechanical
blends
Apparent Molecular Weight Distributions in Bituminous Binders
No full textMolecular weight distributions are widely used to evaluate the effects of aging or modifiers in bituminous binders. As with polymers, the most common techniques to obtain the distributions can be subdivided into two main groups, depending on whether or not they use a solvent. In the first group, the dimension of the molecules is evaluated in a diluted unperturbed state, while, in the second, the dimension derives from the bulk, where aggregated or interacting molecules may behave as single entities. However, the calibration curves used in the bulk are tuned in order to homogenize the results derived from the two approaches. This sort of contradiction, plus the high number of experimental uncertainties, suggest that the term “apparent” should be used for both distributions. These aspects are well known in the field of polymers but have received less attention in the case of bitumens, which are even more complex. This paper pinpoints the advantages and disadvantages of the two techniques, thus highlighting the most appropriate use. Bulk methods are preferred when evaluating properties that are strictly dependent on the microstructure, such as the level of aging and the effects of additives or modifiers. Diluted methods should be used when the molecular size matters, such as in quantifying the presence of polymers or rejuvenators. Both techniques should be used for comparative studies only
Apparent Molecular Weight Distributions for Investigating Aging in Polymer-Modified Bitumen
No full textThe oxidative aging of bituminous binders affects the performance and durability of pavements. In the case of polymer-modified binders, aging involves both bitumen and polymers and has a strong impact on the whole architecture of the material. Rheology may help in understanding these structural changes, and interesting information may be obtained by analysing the evolution of apparent molecular weight distributions. This was demonstrated with a bituminous binder modified with a poly(styrene-butadiene) block copolymer and subjected to prolonged artificial aging. Isothermal frequency sweep tests were used to construct master curves of the phase angle and magnitude of the complex modulus. The master curves were then used to calculate relaxation spectra and apparent molecular weight distributions of the binders, as well as simulated temperature sweep tests. A comparison of the behaviour of the base and modified bitumen highlighted the role of the polymer in aging. Polymer degradation significantly damages the elastomeric network, yet the residual polymer chains still interact with the bitumen molecules and reduce their oxidative aging. The apparent molecular weight distributions were deconvoluted to create an aging index specifically developed for polymer-modified bitumen
Wood Residue-Derived Biochar as a Low-Cost, Lubricating Filler in Poly(butylene succinate-co-adipate) Biocomposites
Full text linkThis study focused on the development of a novel biocomposite material formed by a thermoplastic biodegradable polyester, poly(butylene succinate-co-adipate) (PBSA), and a carbonaceous filler as biochar (BC) derived by the pyrolysis of woody biomass waste. Composites with various BC contents (5, 10, 15, and 20 wt.%) were obtained by melt extrusion and investigated in terms of their processability, thermal, rheological, and mechanical properties. In all the composites, BC lowered melt viscosity, behaving as a lubricant, and enhancing composite extrudability and injection moulding at high temperatures up to 20 wt.% of biochar. While the use of biochar did not significantly change composite thermal stability, it increased its stiffness (Young modulus). Differential scanning calorimeter (DSC) revealed the presence of a second crystal phase induced by the filler addition. Furthermore, results suggest that biochar may form a particle network that hinders polymer chain disentanglement, reducing polymer flexibility. A biochar content of 10 wt.% was selected as the best trade-off concentration to improve the composite processability and cost competitiveness without compromising excessively the tensile properties. The findings support the use of biochar as a sustainable renewable filler and pigment for PBSA. Biochar is a suitable candidate to replace more traditional carbon black pigments for the production of biodegradable and inexpensive innovative PBSA composites with potential fertilizing properties to be used in agricultural applications
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