查看更多>>摘要：The fusion of additive layers is the primary concern, which affects the mechanical properties of the three-dimensional printed structures prepared by material extrusion-based additive manufacturing (MEAM) process. To promote the fusion and strength between the thermoplastic layers during MEAM process, the metal spray in between the additive layers is used as a novel approach. In this study, aluminium (Al) spray has been deposited in between the polylactic acid structures to enhance the bonding of the additive layers. The methodology includes deposition of 1, 3 and 5 Al spray layers at periodic time intervals with varying infill percentage (40%, 70% and 100%) and bed temperature (60 degrees C, 80 degrees C and 100 degrees C). The structures have been subjected to flexural testing for investigation of the role of each input process parameter followed by fracture morphology analysis through scanning electron microscopy and energy-dispersive spectroscopy. The results of the study suggested that the maximum flexural strength is possible with five spray layers, 70% infill and 100 degrees C bed temperature.
Rodrigues, Elton Jorge da RochaCavalcante, Maxwell de PaulaDutra Filho, Jose CarlosTavares, Maria Ines Bruno...
14页
查看更多>>摘要：Silica-based (SiO2) poly(3-hydroxybutyrate) (PHB) nanocomposites were obtained via an in situ sol-gel route in three distinct particle concentrations (1, 5, and 7.5% by weight of PHB). The polymer hybrids formed were analyzed via wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), Fourier transform infrared (FTIR) spectroscopy, and time-domain nuclear magnetic resonance relaxometry (TD-NMR). The SiO(2)inorganic structure displayed surface fractal features at low concentration (1 wt%) and denser agglomerates at higher concentrations (5 and 7.5 wt%). FTIR and SAXS results confirmed the formation of the inorganic matrix amid the polymer chains with different levels of distribution and organization. WAXD and TD-NMR results suggested the SiO(2)influence on the PHB crystallinity degree, which was reflected on the polymer's molecular dynamics with a nonlinear dependence of particles concentration in the PHB matrix.
查看更多>>摘要：Glass fiber/polymerized cyclic butylene terephthalate (GF/pCBT) and its nanosilica-modified thermoplastic composites were manufactured via vacuum-assisted molding pressing process. Subsequently, the effects of temperature and nanosilica fillers on the macroscopic mechanical behavior of glass fiber-reinforced pCBT composites were discussed. Failure morphologies of specimens were observed by scanning electron microscopy (SEM). Experimental results show that pure GF/pCBT composites have good mechanical properties, whereas their half-strength degradation temperature (T-S= 0.5) is relatively lower. It is also found that nanosilica-modified composites have higher heat resistance performance, andT(S)= 0.5 point of the modified composites enhanced by 10 degrees C. SEM observations show that the smooth fracture surface in the broken composites appears at higher temperatures, which indicates that the toughness of nanosilica-modified GF/pCBT composites is improved.
Dong, Dang ThuyNam, Vu HoaiTrung, Nguyen ThoiPhuong, Nguyen Thi...
27页
查看更多>>摘要：In this article, the nonlinear thermomechanical buckling behaviors of sandwich functionally graded plates subjected to an axial compression and external pressure are analytically analyzed resting on nonlinear elastic foundation. Assuming that the plates are reinforced by oblique stiffeners and rested on nonlinear elastic foundation. The formulations are established using the higher-order shear deformation theory taking into account the geometrical nonlinearity of von Karman. The Lekhnitskii's smeared stiffener technique is developed for shear deformable oblique stiffener system using the coordinate transformation technique with both mechanical and thermal terms. The Galerkin method is utilized to obtain the nonlinear algebraically equation system, then, solve it to determine the explicit expressions of critical buckling loads and postbuckling load-deflection curves. Numerical results show the effects of temperature, nonlinear elastic foundation, stiffeners, and material and geometrical properties on nonlinear behaviors of plates.
查看更多>>摘要：The nanocomposites of high-density polyethylene, low-density polyethylene, polypropylene, and poly(vinyl chloride) reinforced withAzadirachta indicawood flour (WF) and different amounts of the organomodified nanoclay and titanium dioxide (TiO2) nanopowder were produced by melt-blending process followed by compression molding. Polyethylene-co-glycidyl methacrylate (PE-co-GMA) was used as a compatibilizer. TiO(2)nanopowder was synthesized by sol-gel method and characterized using transmission electron microscopy (TEM). The average size of the synthesized nano-TiO(2)was 17.5 nm, which was confirmed both by TEM and X-ray diffraction (XRD) study. The distribution of nanoparticles in the nanocomposites was also examined by the XRD study. The surface modification of the TiO(2)nanoparticles by organic surfactant cetyl trimethyl ammonium bromide and their interaction with the wood and the polymer were studied by Fourier transform infrared spectroscopy. Incorporation of compatibilizer PE-co-GMA, nanoclay, and nano-TiO(2)significantly influenced the mechanical and thermal properties of the WF-reinforced composites. Wood polymer composites (WPC) reinforced with nanoclay and nano-TiO(2)showed improved tensile strength, tensile modulus, flexural strength, flexural modulus, and hardness. Maximum improvement in mechanical properties was shown by WPC loaded with 40 phr WF, 2 phr nanoclay, and 2 phr of nano-TiO2. On inclusion of organically modified nanoclay and nano-TiO2, the WPC samples showed lower water uptake and higher chemical resistance. The nanocomposites were further examined by TEM study and thermogravimetric analyzer.
查看更多>>摘要：Well dispersed polyethylene (PE) nanocomposites were developed. Montmorillonite (MMT) as aluminosilicate clay layers was modified using organic silanes of different side chains. The MMT was grafted using 3-(trimethoxysilyl)propylamine,N-[3-(trimethoxysilyl)propyl]ethylenediamine, and trimethoxyvinylsilane. The modification process of MMT using organic different silanes was elucidated using microscopic, thermogravimetric, spectroscopic, and X-ray diffraction tools. Then, the developed organoclays were dispersed uniformly in PE matrix producing well exfoliated and dispersed polymer nanocomposites. The mass loadings of dispersed organoclay were varied and the impact of organic silane structure was studied. Thermal stability and flammability properties of the developed polymer nanocomposites were evaluated. The peak heat release rate and average heat release rate were reduced by 48% and 61%, respectively compared to virgin polymer. Also, the average mass loss rate was significantly reduced by 50%. This is in addition to reduction in emission of carbon monoxide (CO) and carbon dioxide (CO2) by 45% and 56%, respectively. The effect of side chain of organosilane on the performance of modified clay layers was studied. The toxicity of gases evolved during combustion process of PE and their polymer nanocomposites were evaluated using Fourier transform infrared connected to cone calorimeter. Additionally, the influence of organic silane on the pyrolysis and toxic gases emission was further studied.
查看更多>>摘要：The zinc oxide (ZnO)-reinforced polylactic acid (PLA) matrix has established shape memory characteristics. But hitherto little has been reported on two-way programmed 3D-printed ZnO-reinforced PLA functional prototypes (prepared on commercial fused deposition modelling (FDM) set-up). This article reports the effect of 3D printing process parameters on tensile, thermal, morphological and two-way programmed shape memory characteristics of ZnO-reinforced PLA-based functional prototypes. It has been ascertained that the maximum strength at peak (14.32 MPa) and maximum strength at break (12.89 MPa) were observed for sample printed at 80% infill density, four number of perimeters with triangular pattern. Maximum Young's modulus (233.68 MPa) was observed for samples printed at 80% infill density and three perimeters with honeycomb pattern. Also, the maximum modulus of toughness (0.883 MPa) was observed in case of sample printed at 80% infill density, five perimeters with rectilinear pattern. Further based upon thermal analysis using differential scanning calorimetry, it has been ascertained that there is no significant effect of FDM process parameters on normalized heat capacity of functional prototype. As regards to two-way programmed specimens, it has been observed that the porosity of functional prototypes increase with 30 min immersion in water as stimulus at 70 degrees C and it again decreases (regain) after 30 min exposure at atmospheric temperature. Contrary to this, the samples' porosity values decrease with 30 min immersion in water at 10 degrees C and regain after 30 min exposure at atmospheric temperature. Further some effect of shape memory has been noticed on functional prototypes volume and weight at two different temperatures.
查看更多>>摘要：The use of wastes in the development of useful material is a key aspect of solid waste management. The aim of this study was to utilize biochar from elephant grass (Pennisetum purpureum) as fillers in polystyrene composites with focus on the morphological and thermal properties of the developed composites. The composites were prepared by hand lay-up technique. The prepared resin and final composite were characterized using scanning electron microscopy, differential scanning calorimetry and Fourier-transform infrared spectroscopy. The biochar also did not contain any reactive hydrophilic groups, thus, it is compatible with polystyrene. Estimated heat capacities of the composites from the thermal test results showed that to obtain a composite of heat capacity range between 600 J/kg center dot K and 760 J/kg center dot K, a 10-30 wt% range of biochar composition should be maintained. At 30 wt% biochar composition, heat capacity was at a maximum value of 757.66 J/kg center dot K.
查看更多>>摘要：Nonisothermal crystallization kinetics of ethylene-acrylic acid copolymer (EAA) and thermoplastic vulcanizate (TPV) based on EAA/chloroprene rubber (CR) were extensively studied using differential scanning calorimetry. Several methods, including the Avrami, Ozawa, and Mo equations, were carried out to analyze the process of nonisothermal crystallization kinetics of EAA and EAA/CR TPV. The results showed that the Avrami analysis modified by Jeziorny and a method developed by Mo could describe the nonisothermal crystallizations of pure EAA and the EAA/CR TPV very well. However, the Ozawa analysis did not give an adequate description. The crystallization processes of pure EAA and the EAA/CR TPV were accelerated by increasing the cooling rates. Moreover, the initial crystallization temperature and the crystallization termination temperature of EAA/CR TPV were higher than those of pure EAA at the same cooling rate, thus showing the nucleating function of CR in the beginning. While the crystallization half time of EAA/CR TPV was apparently longer than that of pure EAA, meaning that the more CR could cause the steric effect and retard the crystallization process of the TPV during the late stages of crystallizing. Although the CR phase of EAA/CR TPV could provide more nucleation sites, the presence of more CR phase must impose a much more significant confinement effect on the crystal growth of EAA. It was believed that this confinement effect overweighed the nucleation effect, thereby slowing down the overall crystallization rate.
查看更多>>摘要：In this study, 5%, 10%, and 15% vermiculite was added to the rigid polyurethane (PU) structure as a fire retardant. The scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), limiting oxygen index, thermal gravimetric analysis, differential scanning calorimetric (DSC) curves, and combustion behavior of the composite materials were investigated. When SEM/EDS analyses were examined, it was observed that surface morphology was affected by the amount of additive material. When XRD analyses were examined, peaks appeared in three different groups. Thermogravimetric analysis was used to determine the thermal stability of PU material with the addition of vermiculite. When the DSC analysis was examined, four temperature zones were obtained. The combustion behaviors of the vermiculite added PU samples with single-flame source and the flammability classes were determined with TS EN ISO 11925-2 standard. It can be said that the usage of inorganic mineral, which is harmless to the environment, can enhance the thermal stability of the material and also reduce the cost of production.
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