Ali Karimi

Kenaf bast cellulosic fibers hierarchy: a comprehensive approach from micro to nano.

Cellulosic fibers from kenaf bast were isolated in three distinct stages. Initially raw kenaf bast fibers were subjected to an alkali pulping process. Then pulped fibers undergone a bleaching process and finally both pulped and bleached fibers were separated into their constituent nanoscale cellulosic fibers by mechanical shearing. The influence of each treatment on the chemical composition of fibers was investigated. Moreover morphology, functional groups, crystallinity, and thermal behavior of fiber hierarchy at different stages of purification were studied using scanning and transmission electron microscopies, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA), respectively. Microscopy studies revealed that applied procedures successfully isolated nanoscale cellulosic fibers from both unbleached and bleached pulps. Chemical composition analysis and FTIR spectroscopy showed that lignin and hemicellulose were almost entirely removed by the applied treatments. XRD and TGA analyses demonstrated progressive enhancement of properties in fibers, hierarchically, in going from micro to nano scale. Interestingly no significant evolution was observed between obtained data of characterized ubnleached and bleached nanofibers.

Oxygen mass transfer in a stirred tank bioreactor using different impeller configurations for environmental purposes

In this study, a miniature stirred tank bioreactor was designed for treatment of waste gas containing benzene, toluene and xylene. Oxygen mass transfer characteristics for various twin and single-impeller systems were investigated for 6 configurations in a vessel with 10 cm of inner diameter and working volume of 1.77L. Three types of impellers, namely, Rushton turbine, Pitched 4blades and Pitched 2blades impellers with downward pumping have been used. Deionized water was used as a liquid phase. With respect to other independent variables such as agitation speed, aeration rate, type of sparger, number of impellers, the relative performance of these impellers was assessed by comparing the values of (KLa) as a key parameter. Based on the experimental data, empirical correlations as a function of the operational conditions have been proposed, to study the oxygen transfer rates from air bubbles generated in the bioreactor. It was shown that twin Rushton turbine configuration demonstrates superior performance (23% to 77% enhancement in KLa) compared with other impeller compositions and that sparger type has negligible effect on oxygen mass transfer rate. Agitation speeds of 400 to 800 rpm were the most efficient speeds for oxygen mass transfer in the stirred bioreactor.

Effects of dissolution of some lignocellulosic materials with ionic liquids as green solvents on mechanical and physical properties of composite films.

In this study two imidazole-based ionic liquids (ILs), namely 1-butyl-3-methyl-1-imidazolium chloride ([BMIM]Cl) and 1,3-methyl imidazolium dimethyl sulfate ([DiMIM][MeSO4]), were used to dissolve ball-milled poplar wood (PW), chemi-mechanical pulp (CMP), and cotton linter (CEL). A set of comparative experiments was carried out, and physical and mechanical properties of the composite films from three different raw materials were determined by means of optical transparency (OT), scanning electron microscopy (SEM), water absorption (WA), thickness swelling (TS), water vapor permeability (WVP), and tensile strength (σb). The overall evaluation indicates the inability of [DiMIM][MeSO4] in complete dissolution of lignocellulosic materials, and sample treatment with this solvent did not lead to water soluble degradation products. However, dissolution trials using [BMIM]Cl were able to dissolve all used lignocellulosic materials by destroying inter and intramolecular hydrogen bonds between lignocelluloses. The OT, WA, TS, and σb of regenerated CEL films were much higher than those of CMP and PW composites. In addition, CEL film showed the lowest WVP compared to WF and CMP composite films. This work demonstrated a promising route for the preparation of biodegradable green cellulose composite films.

Reaction wood drying kinetics: tension wood in Fagus sylvatica and compression wood in Picea abies.

The drying kinetics of reaction woods in Picea abies (compression wood) and Fagus sylvatica (tension wood) in comparison with their corresponding normal woods was investigated under constant convective drying conditions. Moisture profiles along the thickness of small flat-sawn boards taken from reaction and opposite wood zones were evaluated using a polychromatic X-ray system, a non-destructive method. The results revealed substantial differences in the drying behavior between the reaction and opposite woods. Both reaction woods represented slower drying rate than their matching normal woods mainly during the period of free water loss. However, the reaction and opposite woods reached the final moisture content (MC) of about 12% at the same time due to higher initial MC in the opposite woods. In the case of reaction wood, it took a longer time for the moisture profile to become approximately uniform. Overall, a more striking difference was observed in the drying behavior of compression and opposite wood in P. abies. Some important anatomical differences like the cell and pit dimensions and their proportion give some explanations for these drying behaviors.

Preparation of cellulose/polyvinyl alcohol biocomposite films using 1-n-butyl-3-methylimidazolium chloride.

This study has been focused on developing cellulose/polyvinyl alcohol (PVA), a biocomposite film, pretreated with 1-n-butyl-3-methylimidazolium chloride ([bmim]Cl). The dissolved polymers were blended and their biocomposite films including cellulose and cellulose/PVA were prepared. The effect of PVA composition with cellulose was evaluated by comparing the physical, mechanical, chemical and thermal characteristics of produced films with neat cellulosic film. The results showed that the ionic liquid had a great capability in dissolving the polymers. Furthermore, in composition of the raw cellulose some chemical bonds were incorporated between the two components. Water uptake, thickness swelling and water vapor permeability of blend films were increased comparing to cellulosic film. Mechanical strength and Youngs modulus of the films made of cellulose/PVA were decreased while the strain at break was increased. The optical transparency and thermal properties of the blend films were almost the same as neat cellulosic film. This work demonstrated a promising route for the preparation of biodegradable green composites. In addition, this biocomposite film is composed of sustainable biodegradable resources, which is suitable for release to the environment. The biocomposite films showed good optical transparency, thermal stabilities properties.

Noise induced hearing loss risk assessment in truck drivers

Hearing sense is one of the key elements which may have impact on the drivers task quality. This cross-sectional study investigates the hearing status of 500 truck drivers by pure tone audiometry (AC) in one of the cities in Fars province, Iran. Hearing threshold levels of the subjects were measured in frequencies of 500Hz-8000Hz. Screening and determination of permanent threshold shift (PTS) was the first aim of this study. Hence tests were done at least 16 hours after any exposure to noticeable sound. The effect of age as a confounding factor was considered using ISO equation and subtracted from whole hearing threshold. The threshold of 25 dB HL and above was considered abnormal but the calculation of hearing was also carried out using 0 dB HL as reference. Subjects were categorized into two groups on the basis of working experience and the hearing threshold of 25 dB was considered a boundary of normal hearing sense. The results of Pearson Chi-Square test showed that working experience as an independent variable has significant contributing effect on hearing thresholds of truck drivers in frequencies of 500, 1000, 2000 and 4000 Hz (p greater than 0.05). Also, it was shown that currently nine and 12.6 % of truck drivers suffer from impaired hearing sense in left and right respectively (hearing threshold level greater than 25 dB) in mid frequencies (500, 1000, 2000 Hz) and 45% in high frequencies of both ears (4000 and 8000 Hz). The results indicated that hearing damage of professional drivers was expected to occur sooner at 4000 and 8000 Hz than lower frequencies. Finally it was deduced that the occupational conditions of truck drivers may have bilateral, symmetrical harmful effect on hearing threshold sense in all frequencies mainly in frequency of 4000 Hz, so health surveillance programs such as education and periodic medical examinations are emphasized for pre-diagnosing and prevention of any possible impairment and an urgent need to take up some interventions such as better maintenance of roads, automobile industry efforts to reduce the noise level emission of vehicles and reducing number of working hours per day of drivers are highlighted to improve the harmful working conditions of truck drivers.

FLUID MIGRATION IN TWO SPECIES OF BEECH (FAGUS SILVATICA AND FAGUS ORIENTALIS): A PERCOLATION MODEL ABLE TO ACCOUNT FOR MACROSCOPIC MEASUREMENTS AND ANATOMICAL OBSERVATIONS

The aim of this study is to visualise, measure and understand the pathway of liquid and gas at both macroscopic and microscopic levels on specimens of beech ( Fagus silvatica and Fagus orientalis ). The permeability to air and to water has been measured using devices developed in our laboratory. The extension of the area coloured by dyed water is available as well. At the microscopic level, the permeability has been calculated using Poiseuilles equation from the vessel diameters determined on cross sections by image processing. Using dyed water, the proportion of active vessels is also reported at different distances from the injection surface. Our data confirm that the permeability decreases significantly when the sample distance increases. Moreover, the value extrapolated for a zero-length sample is similar to the value predicted from the vessel diameters. This observation stands for both for sapwood and heartwood, in spite of the great permeability difference noticed between these zones. At the microscopic level, the percentage of active vessels decreases with the increase of sample total length and the increase of the distance from the injection point. Several simulations performed using a bond percolation model confirmed our experimental results obtained at the macroscopic and microscopic levels Key words : Air; Beech; Length effect; Liquid; Percolation model; Permeability; anatomy.

Biodegradation of high concentrations of benzene vapors in a two phase partition stirred tank bioreactor

The present study examined the biodegradation rate of benzene vapors in a two phase stirred tank bioreactor by a bacterial consortium obtained from wastewater of an oil industry refinery house. Initially, the ability of the microbial consortium for degrading benzene was evaluated before running the bioreactor. The gaseous samples from inlet and outlet of bioreactor were directly injected into a gas chromatograph to determine benzene concentrations. Carbone oxide concentration at the inlet and outlet of bioreactor were also measured with a CO2 meter to determine the mineralization rate of benzene. Influence of the second non-aqueous phase (silicon oil) has been emphasized, so at the first stage the removal efficiency (RE) and elimination capacity (EC) of benzene vapors were evaluated without any organic phase and in the second stage, 10% of silicon oil was added to bioreactor media as an organic phase. Addition of silicon oil increased the biodegradation performance up to an inlet loading of 5580 mg/m3, a condition at which, the elimination capacity and removal efficiency were 181 g/m3/h and 95% respectively. The elimination rate of benzene increased by 38% in the presence of 10% of silicone oil. The finding of this study demonstrated that two phase partition bioreactors (TPPBs) are potentially effective tools for the treatment of gas streams contaminated with high concentrations of poorly water soluble organic contaminant, such as benzene.

Study on the effects of wood flour geometry on physical and mechanical properties of wood-plastic composites.

The present study is focused on the effects of the shape and size of Fagus orientalis wood flour on physical and mechanical properties of HDPE based wood plastic composites (WPC). Variables included two mesh sizes (20 and 60), as well as five different contents of ground shavings (0, 25, 50, 75, and 100%) mixed with sawdust; totally 10 treatments. HDPT content was 40% in all formulations. Panels were compression molded and physical and mechanical tests were carried out in accordance with ASTM D2240 standard specifications. Results showed that mesh size can only significantly affect the hardness in the studied wood-plastic composites. On the other hand, increasing the proportion of the ground shavings possessing higher aspect ratio (l/d) increased both flexural strength and hardness. This increasing effect however was not observed for ground shavings beyond 50%. It was also concluded that while the addition of ground shavings up to 50% could improve the mechanical properties, higher proportions would reduce some of the properties, particularly the impact strength. In was concluded that the panel made of 50% wood flour combined with 50% ground shavings exhibited overall suitable properties for most applications.

A correlation between the gas and liquid permeabilities of beech wood heat-treated in hot water and steam mediums

Heat-treatment, a major method of wood modification for improving dimensional stability and natural durability, has been studied considerably in the scientific literature. This study will focus on the effect of heat-treatment on permeability, an important physical property of wood by subjecting beech samples to two different mediums of hot water and steam, as well as in two buffered hot water of pH 7 and 8. Hydrothermal treatment caused gas permeability to decrease to its lowest value among the treatments (91.6% decrease comparing the control treatment). Hydrothermal treatment in buffered hot water of pH 8 made the lowest impact on gas permeability (12.3% decrease). The decrease in gas permeability was due to settlement of extractives on vessel perforation plates. Gas permeability showed a highly significant correlation with the amount of swelling in radial direction. Low correlation was found between liquid permeability with water absorption and the amount of swelling. Gas permeability is considered a suitable criterion for predicting the amount of swelling in beech wood.