Characterization of kraft pulp delignification using sodium dithionite as bleaching agent

Abstract

The delignification of kraft pulp with sodium dithionite was studied to remove lignin content in the pulp. The sodium dithionite dissolves the chromophoric groups and residual lignin present in the pulp. The increase in dosage of sodium dithionite and reaction temperature of delignification has positive effect on kappa reduction of pulp. X ray diffraction was used to determine the crystallinity index of bleached pulp. The crystallinity increased from 83.3% for unbleached pulp to 86.7% after delignification. Fourier transform infrared spectroscopy shows the reduction in hydrogen bonding in bleached pulp and also the conversion of cellulose I to cellulose II. FT-Raman spectra shows that the fluorescence observed in the spectra of unbleached pulp reduced significantly in comparison to the spectra of bleached pulp resulting in removal of residual lignin and chromophoric groups present in the pulp. Scanning electron imaging shows the smoothening of fiber surface after bleaching. The delignification reaction followed first-order kinetics and activation energy is 33.57kJ/mol.     

Ageing Effect on Ethyl Cellulose Films

The effect of physical ageing on the electrical properties, such as thermally stimulated discharge currents (TSDC) and conduction currents, of ethyl cellulose (EC) has been analysed. The TSDC thermograms of EC samples, poled with 100kVcm^-1 at different poling temperatures (i.e. 50, 70 and 90°C) consist of two peaks located at 70±5°C and 110±5°C, respectively. The conductivity measurements were made over a time period of 10¹–10³min in the temperature range 30–125°C with a poling field of 100kVcm^-1. It has been observed that physical ageing considerably affects the magnitude of the thermally stimulated depolarization and conduction currents of EC films. This ageing effect, which has been attributed to continuous vitrification of a polymer, is considered to enhance the life-time of a polymer electret. © of SCI.     

Graft copolymerization of 2-vinyl pyridine and styrene onto isotactic polypropylene powder by the preirradiation method

Preirradiated isotactic polypropylene (IPP) powder has been modified by grafting 2-vinyl pyridine (2-VP) and styrene (Sty) in an aqueous medium. The graft copolymerization reaction was studied under different experimental conditions such as total dose, monomer concentration, amount of the solvent, time of reaction and temperature to determine the optimum conditions for affording maximum percentage of grafting (P_g). Maximum grafting percent of 2-VP (180%) and styrene (117%) was obtained under optimum conditions. The rate of grafting (R_g) of 2-VP and styrene has also been determined as a function of total dose, initial monomer concentration and the reaction temperature. From maximum P_g and different R_g values of 2-VP and Sty, 2-VP is more reactive towards grafting as compared to styrene under optimum conditions. Characterization of the graft copolymers is based on differential scanning calorimetric (DSC) analysis. Isolation of the grafted poly(2-VP) and poly(styrene) chains from the grafted samples provides an additional evidence of formation of the graft copolymer.     

Globally Constrained Power Control Across Multiple Channels in Wireless Data Networks

We investigate multi-channel transmission schemes for packetized wireless data networks. The transmitting unit transmits concurrently in several orthogonal channels (for example, distinct FDMA bands or CDMA codes) with randomly fluctuating interference and there is a global constraint on the total power transmitted across all channels at any time slot. Incoming packets to the transmitter are queued up in separate buffers, depending on the channel they are to be transmitted in. In each time slot, one packet can be transmitted in each channel from its corresponding queue. The issue is how much power to transmit in each channel, given the interference in it and the packet backlog, so as to optimize various power and delay costs associated with the system. We formulate the general problem taking a dynamic programming approach. Through structural decompositions of the problem, we design practical novel algorithms for allocating power to various channels under the global power constraint.     

Embedded Tenures: Private Renting and Housing Policy in Surat,India

Over the past two decades, urban housing research in poorer countries has drawn attention to the importance and significance of rental housing. Increasingly, this is also being recognised by international development agencies such as the World Bank and the United Nations Centre for Human Settlements (Habitat). However, the housing policies of national governments have been resilient to change–the conferring of ownership rights is preferred to attempts at fostering a range of tenure options. Drawing upon primary research in Surat, the second largest city in the western Indian state of Gujarat, this paper argues that this is in part the result of complex economic, social and political processes embedded in the relations of production, exchange and consumption of rental housing, which in turn raises questions as to how best poorer landlords are to be supported.     

Selective deposition of a thin copper film for metallization on silicon by the chemical bath process

Recently copper as metallization for contact and interconnect in VLSI is attracting attention. In this study, copper has been selectively deposited over defined areas on glass and silicon using the chemical bath deposition technique. A continuous copper film with a resistivity of 1.87 μΩ cm for 6000 Å thickness is formed. The rate of deposition and the film resistivity are studied. The deposition process and its characteristics are discussed.     

Immobilization of yeast alcohol dehydrogenase by entrapment and covalent binding to polymeric supports

Yeast alcohol dehydrogenase (YADH), which catalyzes oxidoreductions of a broad spectrum of substrates, was immobilized by entrapping it into a network of a poly(acrylamide‐co‐hydroxyethyl methacrylate) copolymer and was also covalently bound onto porous chitosan beads activated through glutaraldehyde. Maximum retention of YADH activity achieved was 90 and 24% for entrapment and covalent binding, respectively. The results obtained for thermal, storage, and operational stability of entrapped and covalently bound YADH were compared with free YADH. The immobilized enzyme showed improved thermal and storage stability. The immobilized enzymes also retained 50% activity after six and eight cycles. Enzyme‐catalyzed oxidation of ethanol was observed to be diffusion‐controlled through Lineweaver–Burk plots. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1299–1305, 2001     

Influence of block composition on structural,thermal and mechanical properties of novel aliphatic polyester based triblock copolymers

A series of ABA type triblock copolymers [Poly(lactide)-block-poly(hexamethylene 2,3-O-isopropylidene tartarate)-block-poly(lactide)] PLA-b-PHIT-b-PLA based on renewable monomers l-tartaric acid and l-lactide have been synthesized and the effect of the PLA chain length on the properties of the triblock copolymers has been systematically investigated. The block nature of the copolymers was established by differential scanning calorimetry (DSC) which showed two glass transition temperatures (T_g) corresponding to PHIT and PLA blocks. Solution cast films of these triblock copolymers turned out to be brittle in nature and to overcome this, ε-caprolactone was copolymerized with l-lactide to generate a separate series of triblock copolymers [PLA-ran-PCL]-b-PHIT-b-[PLA-ran-PCL]. Our study systematically demonstrates that the PLA-to-PCL ratio in the outer block composition influences the mechanical properties via a delayed post-yield stress drop phenomenon. The study further elaborates the time-synchronized strain-field analysis of the novel triblocks to be a convincing approach for the characterization of micro-deformation modes.     

Relationship between the process parameters and the saturation point in electrophoretic deposition

We used the electrophoretic deposition (EPD) process to fabricate a composite with glass frit and investigated the EPD parameters to find the optimum deposition time by understanding the relationship between the process parameters of zeta potential (ZP), pH, deposition yield and saturation point in a slurry. A binder and a dispersing agent were mixed properly with glass frit (0.2–25 μm, d₅₀ = 8.77 μm) in an ethyl alcohol medium for the preparation of the slurry. The pH and ZP were in an inverse relationship to each other due to the generation of H₃O⁺ ions with the addition of the dispersing agent in the slurry. The acidic nature of the slurry resulted in a decrease of the pH and an increase of the ZP. Otherwise, the pH increased with the addition of the glass frit in the slurry because H₃O⁺ ions were absorbed on the glass frit. Therefore, the OH^? ions correspondingly increased. The saturation point of EPD was strongly correlated with the variation of the pH in the slurry; this is caused by a chemical reaction between the ethyl alcohol and the ions that make up the glass frit. An adjustment of the pH variation and the saturation point in the slurry can be established with respect to the optimum deposition time in the slurry.     

Development of a near activity visual questionnaire to assess accommodating intraocular lenses.

PURPOSE: To develop a questionnaire that subjectively assesses near visual function in patients with 'accommodating' intraocular lenses (IOLs). METHODS: A literature search of existing vision-related quality-of-life instruments identified all questions relating to near visual tasks. Questions were combined if repeated in multiple instruments. Further relevant questions were added and item interpretation confirmed through multidisciplinary consultation and focus groups. A preliminary 19-item questionnaire was presented to 22 subjects at their 4-week visit post first eye phacoemulsification with 'accommodative' IOL implantation, and again 6 and 12 weeks post-operatively. Rasch Analysis, Frequency of Endorsement, and tests of normality (skew and kurtosis) were used to reduce the instrument. Cronbach's alpha and test-retest reliability (intraclass correlation coefficient, ICC) were determined for the final questionnaire. Construct validity was obtained by Pearson's product moment correlation (PPMC) of questionnaire scores to reading acuity (RA) and to Critical Print Size (CPS) reading speed. Criterion validity was obtained by receiver operating characteristic (ROC) curve analysis and dimensionality of the questionnaire was assessed by factor analysis. RESULTS: Rasch Analysis eliminated nine items due to poor fit statistics. The final items have good separation (2.55), internal consistency (Cronbach's alpha=0.97) and test-retest reliability (ICC=0.66). PPMC of questionnaire scores with RA was 0.33, and with CPS reading speed was 0.08. Area under the ROC curve was 0.88 and Factor Analysis revealed one principal factor. CONCLUSION: The pilot data indicates the questionnaire to be internally consistent, reliable and a valid instrument that could be useful for assessing near visual function in patients with 'accommodating' IOLS. The questionnaire will now be expanded to include other types of presbyopic correction.