Evaluation of mechanical properties and durability performance of HDPE-wood composites

The objective of this work is to evaluate the mechanical properties and durability performance of bio-composite materials made from sawdust and thermoplastic polymer (HDPE). For the preparation of the composites, sawdust in different proportions with Maleic Anhydride grafted Polyethylene (MAPE) as the coupling agent was used. The thermal and mechanical properties were successively characterized. The results indicate that adding wood fillers to a polymer matrix increases the degree of crystallinity and improves the tensile strength and ductility of composites. On the contrary, resistance to water absorption decreases as a function of the wood fillers. Scanning electron microscopy (SEM) was used to analyze morphological structure alteration when exposed to intense weathering. The biodegradability of bio-composites up to 97 days was also investigated; the results indicate that, by increasing the filler content, the amount of weight loss increased as well. In other words, even though the addition of sawdust to thermoplastic polymer improves the mechanical performance of a composite material, it also accelerates the biodegradation rate of the composite. An optimum amount of filler content might compromise the effect of biodegradation and mechanical properties of composite materials

First-principles studies of SnS2, MoS2 and WS2 stacked van der Waals hetero-multilayers

We present the energetics, structural and electronic properties of SnS2 monolayer stacked with MoS2 and WS2 monolayers making the van der Waals hetero-layers using the first-principles methods. The exchange-correlation functionals used are the LDA, GGA functionals as well as the newly developed variants of non local van der Waals (vdW) exchange-correlation functionals, namely vdW-DF-revPBE and vdW-DF2-C09. We also considered the combinations of hetero-layers that involve all the three SnS2, MoS2 and WS2 stacked together. All the investigated hetero-layers have a short decay (offset) of the equilibrium lattice parameters compared to the SnS2 single layer one. Except for the GGA-PBE functional, all the functionals predict the interlayer distances closer to the previous theoretical and experimental studies. The hetero-layers that have relative low binding energies are indirect band gap semiconductors, while those with dramatically high binding energies are weakly or strongly metallic. This study gave another avenue of altering the energetics and electronic properties of SnS2 monolayer through vertical stacking with MoS2 and WS2. The variation in band gap enables these newly predicted hetero-layers to be suitable candidates for designing novel devices for nanoelectronic and optoelectronic technology, which includes energy storage, photodetectors, thermophotovoltaic.REM acknowledges University of Pretoria for financial support.http://ees.elsevier.com/cocom/default.asp2019-09-01hj2018Physic

A black‐box automated approach to calibrate numerical simulations and optimize cover design: Application to a flow control layer constructed on an experimental waste rock pile

Mining operations often produce large volumes of waste rock to access economically valuable mineralized zones. Waste rock is usually stored in surface piles, the construction and reclamation of which represent a challenge for the industry. A flow control layer (FCL) made of crushed waste rock or sand and constructed on top of each waste rock bench could contribute to control water infiltration, thus improving waste rock pile stability and limiting contamination. An experimental waste rock pile was built and instrumented at the Tio mine (Rio Tinto Fer et Titane, Canada) to evaluate the performance of an FCL in field conditions. Large infiltration tests and rainfall monitoring were carried out, and measured outflow and water contents were used to calibrate numerical simulations. However, data were noisy and sometimes incomplete, and the models were difficult to calibrate. A new automated calibration approach was therefore proposed. An algorithm was developed to automate the numerical simulation calibration, using a black-box method that involves solving an optimization problem on a function without an analytic form. The approach was applied on measurements obtained from large-scale infiltration tests and validated using 2 yr of field monitoring data. Finally, the automated approach was adapted to optimize the design of the FCL, and an optimal design (material properties and layer thickness) was recommended based on local climate conditions. The proposed automated method could contribute to reduce the bias induced by manual calibration and allows for rapid multivariable calibration and optimization for a broad spectrum of mine waste cover system applications

Structural and electronic properties of SnS2 stacked nanosheets : an ab-initio study

We present an ab-initio study of the structural and electronic properties of SnS2 stacked nanosheets using the standard LDA and GGA functionals as well as the newly developed variants of the non-local van der Waals (vdW) exchange correlation functionals, namely vdW-DF-revPBE and vdW-DF2-C09. We have examined different stacking configurations of the two, three and four SnS2 layers. The GGA-PBE functional fails to describe the interlayer binding energies and interlayer spacing of SnS2 nanosheets, while a good agreement is observed between the calculated and available experimental values when the van der Waals corrected functionals are used, mostly the vdW-DF2-C09. It is found that the interlayer interactions in the SnS2 films are not only vdW type but, the overlap of wave functions of neighboring layers have to be taken into account. We have observed a systematic reduction in the band gap with the increase in the number of stacked layers. This can be another way of controlling the band gap of SnS2 nanosheets as required for electronic devices.http://www.elsevier.com/locate/jpcs2019-09-01hj2018Physic