Suvendu Manna

Enhancement of tensile strength of lignocellulosic jute fibers by alkali-steam treatment.

The physico-chemical properties of jute fibers treated with alkali (NaOH) solution have been investigated in this study. The treatments were applied under ambient and elevated temperatures and high pressure steaming conditions. To the knowledge of these authors the influence of alkali-steam treatment on the uniaxial tensile strength of natural ligno-cellulosic fibers, such as jute, has not been investigated earlier. The results from this investigation indicate that a 30 min dipping of the fibers in 0.5% alkali solution followed by 30 min alkali-steam treatment leads to an increase in the tensile strength of up to 65%. The increase appears to be due to fiber separation and removal of non-cellulosic materials, which, in turn, resulted in an increased crystallinity.

Composition analysis and material characterization of an emulsifying extracellular polysaccharide (EPS) produced by Bacillus megaterium RB-05: a hydrodynamic sediment-attached isolate of freshwater origin.

Aims:  This work was aimed to isolate, purify and characterize an extracellular polysaccharide (EPS) produced by a freshwater dynamic sediment‐attached micro‐organism, Bacillus megaterium RB‐05, and study its emulsifying potential in different hydrocarbon media.

Temperature dependent photoluminescence and electroluminescence characteristics of core-shell Ge–GeO2 nanowires

Ge nanowires of several micrometers long and an average diameter of  ∼70 nm have been grown by the vapour–liquid–solid technique. Different structural characteristics indicate the presence of a Ge core along with a thin (~10 nm) amorphous GeO2 shell layer. The signature of direct as well as indirect band gap emission is observed from the temperature dependent photoluminescence measurements of Ge nanowires. Room temperature near infrared electroluminescence has been achieved from the metal–insulator–semiconductor structure consisting of Ge nanowires. The phonon mediated indirect transition dominates the electroluminescence characteristics above 100 K, whereas a no phonon direct transition at low temperatures makes the device attractive for optical emitters.

Effect of growth temperature and post-growth annealing on luminescence properties of molecular beam epitaxy grown single layer Ge quantum dots

We report the detailed structural and luminescence properties of Si-embedded single layer Ge nanoislands grown via Stranski-Krastanov mechanism using molecular beam epitaxy. The luminescence energy peak positions correlated with structural properties have been studied as a function of the growth temperature and post-growth annealing. The photoluminescence peak for the annealed sample (500 °C grown) is blue shifted with increasing anneal temperature compared to the as grown sample due to intermixing of Si/Ge. Electroluminescence from the single layer Ge islands in the wavelength range 1.53 to 1.67 μm has been demonstrated using a metal-insulator-semiconductor structure, making it attractive for quantum dot light emitting devices.

Effect of photodegradation of lignocellulosic fibers transesterified with vegetable oil

This study presents the assessment of resistance of raw and vegetable oil treated transesterified lignocellulosic fibers (LCFs) such as jute, and sisal against photo-induced oxidation and subsequent hydrolysis reaction by subjecting them to alternate cycles of irradiation of ultraviolet light (UV) of wavelength between 300 to 400 nm and spray of deionized water in an artificial accelerated weathering (AAW) test chamber over a duration of 500 hours. The extent of UV and moisture induced degradation has been evaluated by measuring the residual tensile strength and water absorption before and after AAW. The results indicate that at the end of the 500 h of exposure transesterified LCFs retained about 53 to 60 % of its initial tensile strength, whereas the corresponding retention for raw fibers was only about 14 to 20 %. Average water absorption for transesterified LCFs was increased to about 100–110 % (by weight) following AAW from a pre-exposure value of about 65–80 %. The corresponding average increase for raw LCFs was 300 % from 220 %, respectively. Although both raw and transesterified LCFs exhibited susceptibility to oxidation and hydrolysis following AAW, the resulting impact was found to be more pronounced for raw fibers.

Enhanced biodegradation resistance of biomodified jute fibers

A bio-catalyzed process has been developed for treating jute fibers to enhance their tensile strength and resistance against biodegradation. Lipolytic bacteria were used in the process to transesterify jute fibers by replacing hydrophilic hydroxyl groups within cellulose chains with hydrophobic fatty acyl chains. Transesterification of some of the hydroxyl groups within the fiber was confirmed with FTIR, UV-vis spectroscopy, (13)C solid state NMR, gas chromatography and analytical determination of ester content. Biomodified fibers exhibited remarkably smaller affinity to water and moisture and retained 62% of their initial tensile strengths after being exposed to a composting environment over 21 days. The corresponding figure for untreated fibers was only 30%. Efficacy of the process reported herein in terms of tensile strength and biodegradation resistance enhancement of fibers achieved after treatment appears to be comparable with similar chemical processes and better than the enzyme-catalyzed alternatives.

Biodegradation of chemically modified lignocellulosic sisal fibers: study of the mechanism for enzymatic degradation of cellulose

Abstract The susceptibility and characteristics of biological degradation of lignocellulosic fibers, such as sisal fibers, are presented in this study using a modified soil burial test (SBT) protocol. The biodegradation profile of untreated sisal fibers as well as of fibers treated with an alkaline emulsion of neem oil and phenolic resin was evaluated by estimating the enzymatic activities during the exposure of fibers to a soil/compost mix. Observation of the results indicated that biodegradation of the fibers was predominated by enzymatic hydrolysis of amorphous materials followed by degradation of crystalline cellulose. It was also evident that “oil-resin” treatment makes the fibers more resistant to biodegradation owing to the removal of amorphous materials, enhanced hydrophobicity, and possible chemical alteration of the surface hydroxyl groups of the fiber surface. This research aims to establish a systematic knowledge on the biodegradation profile of fiber components using a state-of-the-art protocol for SBT.

Direct band gap optical emission from Ge islands grown on relaxed Si0.5Ge0.5/Si (100) substrate

Strained Ge islands have been grown on fully relaxed Si0.5Ge0.5 substrate by pulsed laser ablation technique. The formation of strained Ge islands has been found for film with higher thickness following Stranski–Krastanov growth mechanism. The variation of strain with changing Ge layer thickness has been analyzed using Raman spectroscopy and high-resolution X-ray diffraction techniques. X-ray photoelectron spectra have shown the absence of any Si-Ge intermixing and oxidation of Ge films. A strong no-phonon photoluminescence emission from Ge islands has been observed, showing the superior optical characteristics of the islands grown on relaxed substrate.

Fixed bed column study for water defluoridation using neem oil-phenolic resin treated plant bio-sorbent

Fluoride has both detrimental and beneficial effects on living beings depending on the concentration and consumption periods. The study presented in this article investigated the feasibility of using neem oil phenolic resin treated lignocellulosic bio-sorbents for fluoride removal from water through fixed bed column study. Results indicated that treated bio-sorbents could remove fluoride both from synthetic and groundwater with variable bed depth, flow rate, fluoride concentration and column diameter. Data obtained from this study indicated that columns with the thickest bed, lowest flow rate, and fluoride concentration showed best column performance. Bio-sorbents used in this study are regenerable and reusable for more than five cycles. The initial materials cost needed to remove one gram of fluoride also found to be lower than the available alternatives. This makes the process more promising candidate to be used for fluoride removal. In addition, the process is also technically advantageous over the available alternatives.

First-Order Assessment of the Influence of Three EPS and Calcite-Producing Microbes Isolated from a Cemented Sand Site on Soil Shear Strength

Subsurface geotechnical data from a cemented tailings sand site in eastern India indicated that the cementation was at least partially biogenic. Three strains of aerobic soil-residing bacteria from this site exhibited capabilities of producing extracellular polymeric substance, calcite and struvite when grown in minimal mineral salt media. These strains grew easily under a variety of physical, chemical and nutritional conditions. Drained triaxial testing of loose sand samples indicated that they became stronger upon hosting these strains. No details on EPS and calcite production of these isolates and the effects of these products on soil behavior were found in the literature.