Effects of hygrothermal ageing on mechanical properties of flax pulps and their polypropylene matrix composites

The aim of this work was to study the kinetics of water uptake and its influence on mechanical behavior of both flax pulps and their composites with a maleic anhydride polypropylene copolymer (MAPP) modified polypropylene (PP) matrix by immersion in distilled water at 30, 50, 70, and 100°C. Both the influence of two different MAPP compatibilizers and the optimum doses of each ones were analyzed. The kinetics of water uptake was studied from weight measurements at regular interval times. The diffusion coefficient was dependent on the immersion temperature and MAPP content. Tensile modulus and strength of single flax fiber decreased by water immersion. Both flexural strength and modulus of composites decreased as a result of the combined effect of thermal ageing and moisture absorption. MAPP coupling agent increases moisture resistance and mechanical properties for MAPP‐modified systems with respect to the unmodified ones. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3438–3445, 2006     

A comparative study on the influence of epoxy sizings on the mechanical performance of woven carbon fiber-epoxy composites

In the present work the effect of epoxy sizings on the fracture behavior of woven carbon fiber tetrafunctional epoxy composites has been investigated. Three-point flexural, short beam shear (SBS) and Mode-II interlaminar fracture toughness (ENF) tests have been carried out. Wettability and Atomic Force Microscopy (AFM) studies have been performed on commercial sized, desized and 0.7 wt% TGDDM and 0.7 wt% DGEBA sized carbon fibers. Dynamic mechanical thermal analysis and Scanning Electron Microscopy (SEM) studies were also carried out on the different carbon fiber/epoxy composites. The used sizing treatments provided composites with improved mechanical properties due to the enhancement achieved in the fiber-matrix adhesion. Polym. Compos. 25:319–330, 2004. © 2004 Society of Plastics Engineers.     

Office waste paper as cellulose nanocrystal source

Cellulose nanocrystals (CNC) are isolated from office waste paper using an alkali solution and a subsequent acid hydrolysis process. The Fourier transform infrared spectroscopy and X‐ray diffraction (XRD) results demonstrate that ink and fillers used in the papermaking industry are almost totally removed after alkali treatments. The XRD results show that CNCs obtained after 2 wt % NaOH solution treatment and a subsequent hydrolysis process exhibit only a cellulose I crystalline structure, and the crystallinity index value increases around 42% with respect to initial office waste paper. Nevertheless, CNCs obtained after 7.5 wt % NaOH solution treatment and a subsequent acid hydrolysis process show a mixture of cellulose I and cellulose II polymorphs. The thermal analysis shows that the CNCs obtained after 7.5 wt % NaOH solution treatment and a subsequent acid hydrolysis process are thermally less stable than other samples, suggesting that the cellulose chains could depolymerize into low molecular weight sugar compounds. Even though the atomic force microscopy images confirm the presence of CNCs, the optical images show that some cellulose microfibers still maintain their structure. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45257.     

Sensitivity analysis of optimum solutions by updating active constraints: application in aircraft structural design

Often the parameters considered as constants in an optimization problem have some uncertainty and it is interesting to know how the optimum solution is modified when these values are changed. The only way to continue having the optimal solution is to perform a new optimization loop, but this may require a high computational effort if the optimization problem is large. However, there are several procedures to obtain the new optimal design, based on getting the sensitivities of design variables and objective function with respect to a fixed parameter. Most of these methods require obtaining second derivatives which has a significant computational cost. This paper uses the feasible direction-based technique updating the active constraints to obtain the approximate optimum design. This procedure only requires the first derivatives and it is noted that the updating set of active constraints improves the result, making possible a greater fixed parameter variation. This methodology is applied to an example of very common structural optimization problems in technical literature and to a real aircraft structure.     

Influence of the addition of PEG into PCL-based waterborne polyurethane-urea dispersions and films properties

In this work, segmented waterborne polyurethane-urea (WBPUU) dispersions containing hydrophobic polycaprolactone (PCL) and hydrophilic poly(ethylene glycol) (PEG) in different molar ratios are synthesized and used for the subsequent preparation of films by casting. The molar ratio of PEG is gradually increased up to 0.20 in order to analyze the effect of low hydrophilic PEG content (from 1.7 to 7.1 wt %) on the properties of resulting dispersions and films. Regarding the dispersions, the addition of PEG results in an increase of the particle size, from 86 ± 1 in the case of pure PCL-based system to 112 ± 15 for systems containing 7.1 wt % of PEG, as well as in the formation of a core–shell structure in the particles. Films show different behaviors depending on their PEG content. WBPUUs containing just PCL or very low content of PEG in the soft segment present higher stiffness. However, the addition of PEG in a content of 3.4 wt % or higher hinder the ability of the short-range ordering of the hard segment, increasing the elongation at break from 842 ± 102 MPa for PCL-based WBPUU to 1312 ± 84 MPa for the system with the highest PEG content. Systems with higher PEG content form nanoparticles with more segregated core–shell structures inducing to the film a higher hydrophilicity. Hence, the addition of PEG to a PCL-based WBPUU allows to tune the properties of the resulting film increasing the range of application of these materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48847.     

Effect of operating conditions on the drying of fine and ultrafine sand in a fountain confined conical spouted bed

Abstract

A study has been carried out on the influence process conditions and design parameters have on the drying in a conical spouted bed. Optimum parameters have been determined for the draft tube and the fountain confiner. Drying time is reduced when the spout region is enlarged. A distance between the bed surface and the lower end of the confiner in the 0.10–0.15 m range and a confiner of 0.5–0.9 m length minimize the drying time. Longer distances do not avoid entrainment, and shorter distances lead to higher pressure drop and minimum spouting velocity. Longer fountain confiners do not reduce significantly the drying time. Draft tubes with a reduced aperture ratio lead to longer drying times due to their adverse effect on the gas–solid contact. Aperture ratios above 60% cause a decrease in the efficiency of the process due to the higher gas flow rates required to achieve spouting regime.     

亨克尔HE-219 “UHU”

正板件包含大量的灰色塑料件以及丰富的内构例如无线电,座椅,武器等。机身被完美的复原了。引擎的刻画也十分出色。机头的FuG 220无线电天线开的很不错,不过我依然还是用了Master Model的金属件取代了原始板件,主要是因为金属件的材质可以更好的还原真实的天线。非常推荐。     

Kinetic study of the catalytic reforming of biomass pyrolysis volatiles over a commercial Ni/Al2O3 catalyst

An original kinetic model has been proposed for the reforming of the volatiles derived from biomass fast pyrolysis over a commercial Ni/Al₂O₃ catalyst. The pyrolysis-reforming strategy consists of two in-line steps. The pyrolysis step is performed in a conical spouted bed reactor (CSBR) at 500 °C, and the catalytic steam reforming of the volatiles has been carried out in-line in a fluidized bed reactor. The reforming conditions are as follows: 600, 650 and 700 °C; catalyst mass, 0, 1.6, 3.1, 6.3, 9.4 and 12.5 g; steam/biomass ratio, 4, and; time on stream, up to 120 min. The integration of the kinetic equations has been carried out using a code developed in Matlab. The reaction scheme takes into account the individual steps of steam reforming of bio-oil oxygenated compounds, CH₄ and C₂-C₄ hydrocarbons, and the WGS reaction. Moreover, a kinetic equation for deactivation has been derived, in which the bio-oil oxygenated compounds have been considered as the main coke precursors. The kinetic model allows quantifying the effect reforming conditions (temperature, catalyst mass and time on stream) have on product distribution.     

Evolution of the mechanical properties and estimation of the useful lifespan of poly(lactic acid) based compounds

The useful lifespans of a poly(lactic acid)/poly(methyl methacrylate) (PLA/PMMA) 80/20 (wt%) blend and a poly(lactic acid)/dioctyl adipate/talc (PLA/DOA/talc) compound have been estimated by applying an Arrhenius relationship to the evolution of the mechanical properties whilst ageing. The studied PLA based systems showed lower activation energies (ca 8 ? 20 kJ mol^?1) than those reported in the literature for other synthetic thermoplastics, indicating lower thermo‐oxidative stability. However, both systems were interesting choices for semi‐durable applications in terms of useful lifespan estimations. The PLA/PMMA blend showed a drastic loss in stiffness at T_g due to its almost amorphous structure whereas, in contrast, PLA/DOA/talc showed acceptable mechanical properties above its glass transition temperature due to its semicrystalline structure. © 2018 Society of Chemical Industry     

Characterization of Ln4Al2O9 (Ln=Y,Sm, Eu,Gd, Tb) rare-earth aluminates as novel high-temperature barrier materials

A family of cuspidine-type rare-earth (RE) aluminates with the general formula Ln₄Al₂O₉ (Ln= Y, Sm, Eu, Gd, Tb) was prepared for potential use as thermal-barrier coating (TBC) materials with appropriate properties. Various trivalent lanthanides were applied to tailor the properties of the oxides for use as ceramic top coat (TC) materials intended for high-temperature applications. Following various heat treatments, the X-ray diffraction (XRD) results obtained demonstrated that Eu₄Al₂O₉ (EuAM) possessed the greatest structural stability of all the samples at 1200 and 1300?°C. Moreover, Y₄Al₂O₉ (YAM) had a long lifetime at 1000?°C, and was stable at 1100?°C. At 1200?°C, Sm₄Al₂O₉ (SmAM) and Gd₄Al₂O₉ (GdAM) were more stable than Tb₄Al₂O₉ (TbAM). However, at 300–1000?°C, the TbAM exhibited the highest thermal expansion coefficient (TEC) of all the samples. At 600?°C, the thermal diffusivity values of the five compositions were favourable, and were lower than that of yttria-stabilised zirconia (YSZ) oxides.