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The dynamics of gas fluidization is investigated by means of multiresolution analysis. Empirical mode decomposition (EMD) and the Hilbert-Huang transform approach applied to the signals of pressure fluctuation of the bed have been used for this purpose, operating in bubbling and slugging regimes. To elucidate the different components of the different scales, recurrence plots (RP) and recurrence quantification analysis (RQA) have been used. These techniques can distinguish the three different scales of gas fluidization: micro-scale, meso-scale and macro-scale, and classify every mode on its scale. Three modes from the EMD have been related to each dynamic component: particle interaction, local bubble dynamics and bed oscillation, showing evidence of this relationship. To show that the complexity of the modes matches with their characteristics, two measures have been computed: the apparent entropy and Lemped–Ziv complexity.

Spilled oil in seas has a direct impact on the environment and biodiversity. Moreover, there is no clear relationship between the amount of oil in the aquatic environment and its impact, since it mainly depends on the time and season that the oil is spilled. Nowadays, there are several techniques to clean up and recover oil from the sea, including the use of microorganisms, chemicals, controlled burning, dispersants and solidifiers, among others. Sometimes, unfortunately, the best option is to watch and wait for natural attenuation. Cellulose nanofibers have potential environmental applications due to their availability, light weight, mechanical and optical properties, and renewability. Several studies have dealt with modification of their hydrophilic character through silanation and acetylation. Both treatments, despite having a significant impact on the environment, are not plausible on a large scale because of the cost of chemicals and complexity of the modification. In this sense, the present work aims to develop hydrophobic nanocellulose-based aerogels from bleached kraft eucalyptus fibers modified with alkyl ketene dimers. For this, an experimental batch of 24 aerogels was prepared, including three types of CNF (TEMPO-oxidized, enzymatically hydrolyzed and mechanical) and eight modification degrees. The obtained aerogels were characterized in terms of morphology, hydrophilicity and water–oil absorption capacity under static and dynamic conditions, as well as their suitability for recycling and reuse for selective oil removal. The results showed that it is possible to obtain 3D-structured aerogels with a high oil absorption capacity by a simple and presumably low-cost methodology.

The textile industry generates a large amount of byproducts that must be treated before being recycled or disposed of. The treatments to extract the dyeing agents are mandatory, and involve costs and interaction with toxic reagents. A relevant amount of such byproducts are short cotton dyed fibers. Cotton fibers are high-quality cellulosic fibers and can be used as composite reinforcement. In this paper, dyed cotton fibers were used to formulate, obtain and tensile test composite materials. The impact of the presence of dyes was studied and such dyes enhanced the interphase between the matrix and the reinforcement. On the other hand, when a coupling agent was incorporated to the formulation of the composites, the dyes hindered the chemical interactions between the maleic acid and the OH groups of the cellulosic fibers. Nonetheless, the composite materials showed competitive mechanical properties that were better than other natural fiber-reinforced composites and comparable to some glass fiber-based ones. Dyed cotton fibers can be used as reinforcement without further treatment, increasing the value chain of the textile industry and decreasing the chemical treatments necessary to recycle or dispose of dyed textile fibers. © The Author(s) 2018.

Increasing environmental concern in developed countries has supported the search for greener building materials. In this regard, using materials from renewable resources is of great interest, including the case of wood-plastic composites in replacement of fiberglass-reinforced composites. Since in the Mediterranean regions annual plants are more abundant than wood forests, in the present work, agroforestry wastes were used as reinforcing elements in composites. Specifically, rapeseed wastes were used to produce polypropylene copolymer based composites. The mechanical behavior of the resulting composites was studied, as well as the influence of a coupling agent in the formulation. From the results, rapeseed sawdust exhibited reinforcing capacity and was considered a plausible substitute for wood-plastic composites in certain uses. The stiffness of the composites was affected by the coupling agent, as the Young’s Moduli progressed from 3.2 to 4 GPa for the formulation containing 50wt% of rapeseed sawdust. Micromechanical analysis was used to identify the contribution of each phase by means of a modified rule of mixtures and Halpin-Tsai equations. The micromechanical study confirmed the competitive stiffening capability of rapeseed sawdust in composite materials.

Recurrence plots have been used to analyze and characterize the investigated fluidization regimes: bubbling, slugging and turbulent. Recurrence plots can be qualitatively analyzed considering the distribution of their local white areas (LWA) and local bold areas (LBA). The LWA reflect the macro-scale structure in the bed and appreciably increase for slugging regime because of the increase of the bubble phase contribution to the fluidization dynamics. On the other hand, the LBA, reflecting meso-scale and micro-scale structures, decreases. Several recurrence quantification analysis parameters (RQA) have been computed for the different regimes analyzed and the most appropriate ones have been chosen to characterize and classify the fluidization regimes. It has been found out that the determinism (DET), the average diagonal length (L), the laminarity (LAM), the trapping time (TT) and the recurrence time of type 2 (RET2) detect the evolution from bubbling to slugging regime. The evolution from bubbling to turbulent regime can be detected with all the investigated RQA parameters. A combination of two RQA parameters gives an excellent classification map which distinguishes the slugging from the bubbling regime.

The chaotic behavior, that gas–solid fluidization exhibits, has been characterized using the state space analysis. The space trajectories (attractor) of the dynamic system, reconstructed from the experimental time series of pressure fluctuations in the bed, have been described by the commonly used invariants: correlation dimension (CD), largest Lyapunov exponent (Ly) and the Kolmogorov entropy (K). The evolution of these invariants has been evaluated for bubbling, slugging and turbulent regime by analyzing the dependence on the flow regimes investigated. A new correlation has been proposed to predict the K for slugging regime. Due to some uncertainty involved in the delay determination for the attractor reconstruction, an attractor shape descriptor has been introduced. As shape descriptor, the dynamic moments of the attractor have been chosen and the morphological differences on the shape have been analyzed by varying the delay. The fluidization regimes have been characterized by the dynamic moments.

Natural fiber reinforced composites is an emerging area in polymer science. Fibers derived from annual plants are considered a potential substitute for non-renewable synthetic fibers like glass and carbon fibers. The hydrophilic nature of natural fibers affects negatively its adhesion to hydrophobic polymeric matrices. To improve the compatibility between both components a surface modification has been proposed. The aim of the study is the chemical modification of jute fibers using a fatty acid derivate (oleoyl chloride) to confer hydrophobicity and resistance to biofibers. This reaction was applied in swelling and non-swelling solvents, pyridine and dichloromethane, respectively. The formation of ester groups, resulting from the reaction of oleoyl chloride with hydroxyl group of cellulose were studied by elemental analysis (EA) and Fourier Transform infrared spectroscopy (FTIR). The characterization methods applied has proved the chemical interaction between the cellulosic material and the coupling agent. The extent of the reactions evaluated by elemental analysis was calculated using two ratios. Finally electron microscopy was applied to evaluate the surface changes of cellulose fibers after modification process.

In this work, starch-based composites reinforced with jute strands were obtained by injection moulding procedure. The influence of the degree of adhesion at fibre–matrix interface to the mechanical properties of the composites was evaluated. For this purpose, partial delignification of jute strands by means of NaOH treatment was carried out and the mechanical properties of the corresponding composites determined. The alkali treatment resulted in an increase of the strength and stiffness of the jute strand/starch composites. The enhancement was analysed in terms of compatibility and extension of the adhesion at fibre–matrix interface. The application of a blocking reaction to the surface hydroxyl groups of jute strands corroborated the influence of the mechanical properties to the extension of the interfacial adhesion. Thus, higher extension of the hydrogen bonds at fibre–matrix interface gave higher strength and stiffness of the jute strand/starch-based composites.

Hemp strands as natural lignocellulosic fibers are used to reinforce polypropylene composites obtained by injection molding. The aim of this work is to improve the final mechanical properties using simple and cheap treatments. Therefore, a refining process is applied to increase the specific surface and the fibrillation of hemp strands resulting in a better mechanical anchoring and adhesion with the matrix. The hydrophilic nature of the hemp strands is diminished by surface chemical treatment with alkyl ketene dimmer (AKD) in aqueous media. Final mechanical properties of hemp composites are studied and compared to those of glass fiber reinforced polypropylene composites. The fiber length and diameter of fiber reinforcement during processing are also analyzed. The results thus obtained show that the specific mechanical properties at yield of hemp composites may increase 80% of the mechanical properties of glass fiber composites.

The effect of low pressure operation on the fluidization quality of Group B powders has been studied. Pressure fluctuations have been analyzed—using the standard deviation, the power spectral density function (PSDF) and the auto- and cross-correlation functions for operating pressure down to 4 kPa. Low pressures were found to lead to slugging behavior at lower gas velocities than predicted using correlations applicable to higher pressure operation. Although the fluidization quality was found to be little affected by small decreases in pressure below the ambient level, quite drastic decrease on the fluidization quality were observed at the approach to the 4 kPa lower limit investigated in this study.

Experimental results for the expansion of a fluidized bed operating at pressure (1–15 bar) and high temperature (20°–600°C) are presented for particles belonging to groups B and D. The influence of the diverse variables on bed expansion is analysed. Furthermore, a semiempirical model has been developed which allows the prediction of bed expansion as a function of a new parameter, the “expansion coefficient”.

In this work the experimental and numerical techniques employed to estimate the diffusion coefficient of gold(III) in a macroporous particle of resin XAD-2 impregnated with triisobutyl phosphine sulfide (TIBPS) have been described. Batch and column experiments were performed in order to get the necessary experimental results to determine the effective diffusion coefficient, D e . In the studied initial metal concentration range (39.3–196 mg/dm 3 ), D e was found to increase with increasing the initial feed concentration from 1.28×10 −8 to 6.40×10 −8 m 2 /h.

The hydrodynamical behaviour of fluidized beds at reduced pressures is studied. The minimum fluidization velocity is strongly influenced by pressure, decreasing as pressure increases. The well-known equation of Wen and Yu and two equations proposed for the calculation of umf at reduced pressures are tested; the comparison with experimental data shows that they can be applied only over restricted pressure ranges. The relationship between flow rate, pressure and pressure drop at conditions ranging from high vacuum to high pressure is analysed for the different flow regimes (molecular, slip, laminar, transition and turbulent). A generalized equation is found which predicts fairly well the value of umf at vacuum conditions, atmospheric pressure and high pressures.

The main objective of this research was to study the feasibility of incorporating organosolv semi-chemical triticale fibers as the reinforcing element in recycled high density polyethylene (HDPE). In the first step, triticale fibers were characterized in terms of chemical composition and compared with other biomass species (wheat, rye, softwood, and hardwood). Then, organosolv semi-chemical triticale fibers were prepared by the ethanolamine process. These fibers were characterized in terms of its yield, kappa number, fiber length/diameter ratio, fines, and viscosity; the obtained results were compared with those of eucalypt kraft pulp. In the second step, the prepared fibers were examined as a reinforcing element for recycled HDPE composites. Coupled and non-coupled HDPE composites were prepared and tested for tensile properties. Results showed that with the addition of the coupling agent maleated polyethylene (MAPE), the tensile properties of composites were significantly improved, as compared to non-coupled samples and the plain matrix. Furthermore, the influence of MAPE on the interfacial shear strength (IFSS) was studied. The contributions of both fibers and matrix to the composite strength were also studied. This was possible by the use of a numerical iterative method based on the Bowyer-Bader and Kelly-Tyson equations.

The stiffness of a material has high impact when its industrial use is considered. Moreover, this property has interest in the case of short fiber reinforced materials due to its dependence on the orientation of the fibers against the loads. Due to nowadays-environmental concerns, greener alternatives to oil-based composites are under study and development showing some promising results. In this work, a polyamide 11 reinforced with lignocellulosic fiber composite is evaluated as such sustainable alternative. Previous works showed the suitability of PA11-based composites to replace glass fiber reinforced polypropylene. Nonetheless, there is a lack of information about the flexural modulus behavior of these composites. This is of interest because, under some conditions, flexural modulus is more representative of a material behavior than Young's modulus. The flexural moduli of these composites were analyzed under a three point bending test and the results were evaluated from macro and micromechanical points of view. The increment of the modulus with the fiber contents implied a good dispersion of the reinforcements. Nonetheless, the results were lower than those observed for the tensile modulus. This was unexpected due to the anisotropy of the bending test. The micromechanics analysis showed a lower performance of the fiber during the flexural test. These lower results were related with a non-optimal interface or with the non-adequate compression of the fibers. Additionally, the calculus of the void volume showed low void contents.

Two of the drawbacks of using natural-based composites in industrial applications are thermal instability and water uptake capacity. In this work, mechanical wood pulp was used to reinforce polypropylene at a level of 20 to 50 wt. %. Composites were mixed by means of a Brabender internal mixer for both non-coupled and coupled formulations. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to determine the thermal properties of the composites. The water uptake behavior was evaluated by immersion of the composites in water until an equilibrium state was reached. Results of water absorption tests revealed that the amount of water absorption was clearly dependent upon the fiber content. The coupled composites showed lower water absorption compared to the uncoupled composites. The incorporation of mechanical wood pulp into the polypropylene matrix produced a clear nucleating effect by increasing the crystallinity degree of the polymer and also increasing the temperature of polymer degradation. The maximum degradation temperature for stone ground wood pulp–reinforced composites was in the range of 330 to 345 oC.