Poly(lactic acid) crystallization

Poly(lactic acid) is a biobased and compostable thermoplastic polyester that has rapidly evolved into a competitive commodity material over the last decade. One key bottleneck in extending the use of PLA is the control of its crystallinity. Understanding the crystallization behavior is particularly crucial to control PLA's degradation rate, thermal resistance as well as optical, mechanical and barrier properties. PLA crystallization has also been a particularly rich topic from a fundamental point of view because of the existence of the two enantiomeric forms of lactic acid that can be used to control the crystallization rate but also to form high melting point stereocomplex structures. This article presents an overview of the current understanding on the fundamentals of PLA crystallization in quiescent conditions and on the practical means to enhance its rate. Data from the abundant literature on PLA crystallization were compiled and analyzed to provide comprehensive relationships between crystallization kinetics and the main molecular structure characteristics of PLA. In addition, the most promising efforts in enhancing PLA crystallization kinetics through plasticization or heterogeneous nucleation were reviewed.     

A case study on suspended particles in a natural gas urban transmission and distribution network

Suspended particles in the natural gas transmission and distribution network of the city of Kerman, Iran were investigated. Particle concentration and size distribution were measured in different locations of the natural gas pipeline network. Particle samplings were carried out in two seasons: summer, when there is the lowest consumption, and winter, when there is the highest consumption of natural gas. Additional particle characterization was carried out by scanning electron microscopy coupled with energy dispersion X-ray (SEM/EDX) and X-ray diffraction(XRD) analyses. Particle concentration was found to be significantly higher in winter as compared to summer. The range of particle concentrations in summer was from 0.12 mg/Nm³ at the end of the pipeline to 4.7 mg/Nm³ at the network entrance, and from 0.30 mg/Nm³ to 22.1 mg/Nm³ in winter. Particle size distribution showed a higher frequency of smaller particles in winter than in summer. Larger particles were more likely to exist at the network entrance as compared to the exit. The average particle size ranged from 181 μm at the network end to 253 μm at the entrance in summer, and from 74 μm to 209 μm in winter. Particle characterization confirmed the presence of corrosion products in the suspended particles.     

Effect of nucleation and plasticization on the stereocomplex formation between enantiomeric poly(lactic acid)s

The effect of nucleation and plasticization on the stereocomplex formation between poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) was investigated in blends where PDLA is added as a minor phase in a major phase of PLLA. The use of small amounts of PDLA is aimed at creating a high melting point stereocomplex phase that in turn can serve as nucleating agent for the major phase of PLLA. Blends containing 5% PDLA with talc or organic phosphonate as nucleants and polyethylene glycol as plasticizer were prepared via melt-blending. Their crystallization behavior was investigated through Differential Scanning Calorimetry (DSC) using various thermal histories. Two peculiar stereocomplex melting endotherms were found. The peak temperature and enthalpy of these two endotherms were correlated to prior isothermal crystallization temperature. The different endotherms were also associated with two different crystalline morphologies observed by optical microscopy and referred to as Network and Spherulitic morphologies. The influence of plasticization and of heterogeneous nucleation on these morphologies was investigated through optical microscopy and calorimetric observations.     

Carbonized nano/microparticles for enhanced mechanical properties and electromagnetic interference shielding of cementitious materials

In the present work, carbon nano/microparticles obtained by controlled pyrolysis of peanut (PS) and hazelnut (HS) shells are presented. These materials were characterized by Raman spectroscopy and field emissionscanning electron microscopy (FE-SEM). When added to cement paste, up to 1 wt%, these materials led to an increase of the cement matrix flexural strength and of toughness. Moreover, with respect to plain cement, the total increase in electromagnetic radiation shielding effect when adding 0.5 wt% of PS or HS in cement composites is much higher in comparison to the ones reported in the literature for CNTs used in the same content.     

Abrasive Wear Behavior of High Chromium Cast Iron and Hadfield Steel-- A Comparison

 Abstract： Wear properties of two different crushers used for grinding raw materials of cement industry are compared using pin-on-disk wear test. The wear test was carried out with different loads on a pin. Abrasive wear behavior of two alloys was evaluated by comparing mass loss, wear resistance, microhardness and friction coefficient. The microstructure of the specimens was detected using optical microscope. The results showed that abrasive wear of high chromium cast iron is lower than that of Hadfield steel. Due to the presence of M7C3 carbides on the high chromium cast iron matrix, impact crushers exhibited higher friction coefficient.     

Genetic Algorithm�CArtificial Neural Network Modeling of Moisture and Oil Content of Pretreated Fried Mushroom

In this research, the effect of different pretreatments (osmotic dehydration and gum coating) on moisture and oil content of fried mushroom was investigated, and artificial neural network and genetic algorithm were applied for modeling of these parameters during frying. Osmotic dehydration was performed in solution of NaCl with concentrations of 5% and 10%, and methyl cellulose was used for gum coating. Either pretreated or control samples were fried at 150, 170, and 190 °C for 0.5, 1, 2, 3, and 4 min. The results showed that osmotic dehydration and gum coating significantly decreased (0–84%, depending upon the processing conditions) oil content of fried mushrooms. However, moisture content of fried samples diminished as result of osmotic pretreatment and increased by gum coating. An artificial neural network was developed to estimate moisture and oil content of fried mushroom, and genetic algorithm was used to optimize network configuration and learning parameters. The developed genetic algorithm–artificial neural network (GA–ANN) which included 17 hidden neurons could predict moisture and oil content with correlation coefficient of 0.93 and 96%, respectively. These results indicating that GA–ANN model provide an accurate prediction method for moisture and oil content of fried mushroom.     

Effects of Welding and rotational speeds on the Microstructure and Hardness of Friction Stir Welded Single-Phase Brass

This study focuses on the effects of rotational and welding speeds on the microstructure and hardness of joints in friction stir welded single-phase brass. Welds were achieved under low heat input conditions at rotational and welding speeds of 400-800 r/min and 100-300 mm/min, respectively. In order to characterize the obtained welds, optical microscopy and Vickers hardness measurements were taken on the weld cross sections. According to the obtained results, increasing the welding speed and/or decreasing the rotational speed caused the grain size of the stir zone to decrease and, hence, improved the average hardness of this region. These results are discussed with respect to the interplay between the welding parameters and the peak temperature in the weld thermal cycle.     

Comparison of the Microstructure and Mechanical Properties of As-Cast A356/SiC MMC Processed by ARB and CAR Methods

Accumulative roll bonding (ARB) and continual annealing and roll-bonding (CAR) processes were used in this study for improving the microstructure and mechanical properties of the A356/10?vol.% SiC metal matrix composite (MMC) produced by semi-solid metal processing (SSM). The results showed that using the ARB and CAR processes led to the following points: (a) the uniformity of the silicon and silicon carbide in the aluminum matrix improved, (b) the Si particles became finer and more spheroidal in appearance, (c) the porosity disappeared, (d) the bonding quality between the reinforcement and the matrix improved, (e) the particle-free zone disappeared, and therefore (f) the tensile strength (TS), elongation, and formability index of the MMC samples improved. However, it was found that the CAR process is a better method for improvement of microstructure and mechanical properties of as-cast MMC compared to ARB process.     

Effect of processing parameters and glycerin addition on the properties of Al foams

Aluminum foam has been produced by sintering and dissolution processes using NaCl powders as a space holder. In this research, glycerin is used as a novel lubricant along with acetone. The effects of the processing parameters including compacting pressure, sintering temperatures (620, 640 and 650 °C), size, and volume fraction of the space holder, on the physical and mechanical properties of the produced foams have been investigated. Due to segregation of the Al and NaCl powders at high compaction pressures, spalling of Al foams was observed. Meanwhile, adding small amounts of acetone and glycerin to the mixture ensures homogeneity and prevents segregation of dissimilar powders at varying pressure. Moreover, the addition of glycerin provides an improved homogenous stress distribution within the produced foams during mechanical testing, which in turn halts crack propagation. Meanwhile, an alternative technique to remove NaCl particles during the dissolution stage has been proposed. The results showed that high quality foams were successfully produced under a compaction pressure range of 250–265 MPa and sintering temperature of 650 °C.     

An innovative design of septic tank for wastewater treatment and its performance evaluation: An applicable model for developing countries

A study was carried out to evaluate the treatment efficiency of modified model of septic tank(ST)for the treatment of domestic wastewater.The objective was to explore the possibility of increasing the removal efficiency,at household level,thereby reducing cost and treatment burden on city level treatment plants.For this purpose,a bench scale model of ST was prepared and operated continuously for 78 days at different detention times i.e.,48,24 and 12 h and at two reactor temperatures viz.15°C and 25°C.Domestic wastewater was fed to the bench scale ST without pre-settling.Research was conducted under two different arrangements.Firstly,by installing baffles in the bench scale ST(called Run-1 setup),and secondly by installing perforated plates between the baffles(called Run-2 setup).Results demonstrated that Run-2 setup is better than Run-1 setup.Temperature significantly affects the efficiency.Detention time of 24 h was found feasible.Run-2 setup demonstrated a percentage BOD removal of 45%with effluent BOD of 113 mg·L~(-1)at 15°C and 85%removal with effluent BOD of 31 mg·L~(-1)at 25°C.It is concluded that if a modified design of ST using Run-2 setup is provided at household level,the effluent coming out of the house will meet the National Environmental Quality Standards(NEQS)when reactor temperature is close to 25°C.Development authorities are suggested to change their by-laws and make modified ST mandatory for all households.This may significantly reduce the cost and footprint of city level wastewater treatment plants being planned.