Bleaching Efficiency Research Articles

Mechanisms and kinetics of short pulse laser-induced destruction of silver-containing nanoparticles in multicomponent silicate photo-thermo-refractive glass.

Photo-thermo-refractive (PTR) glass is a photosensitive multi-component silicate glass that is commercially used for the recording of volume holographic elements and finds many applications in advanced laser systems. Refractive index decrement in this glass is observed after UV exposure followed by thermal development. This procedure also causes the appearance of Ag-containing particles that can then be optically bleached by using the second harmonic of a Nd:YAG laser. Despite the broad usage of this method, its mechanisms are still unclear. In this paper, a systematic study of the short pulse laser-induced destruction of Ag-containing particles' kinetics versus incident energy per pulse and dosage is presented. We show that no bleaching of Ag-containing particles occurs for an energy density in laser pulses below 0.1 J/cm2 while above 1 J/cm2, the efficiency of bleaching saturates. Efficiency of bleaching depends on the type of particles to be bleached (Ag, AgBr…). Using a simple model of short pulse laser interaction with nanoparticles embedded in glass, the temperature of the Ag-containing particles reached during the laser interaction is shown to be large enough to produce complete dissipation of these particles which is expected to be the main mechanism of short pulse laser-induced destruction of Ag-containing particles.

Effect of H2O2 bleaching with ultrasonication on the properties of thermomechanical pulp and unbleached kraft pulp

H2O2 was used in the final stage of a multistage bleaching process to increase ISO brightness by 2–3%, because of the poor selectivity and bleachability. However, concerns about the environmental load of the bleaching process have led to the efficient use of oxygen-derived compounds, with a concomitant decrease in the quantity of chlorine-derived compounds consumed.In this study, thermomechanical pulp (TMP) and unbleached kraft pulp (UKP) were bleached with H2O2 and ultrasonicated in order to increase the bleaching efficiency, and the effects of some bleaching conditions such as treatment time, treatment concentration, and temperature were determined.The best bleaching efficiency of pulp was obtained using H2O2 with ultrasonication (at 20kHz) of the pulp mixture at 45°C for 30min. The ISO brightness of the bleached pulp increased up to 1.9%, although the bleached pulp yield was slightly reduced to 1.5%. Magnesium sulfate was used as a bleaching stabilizer to increase the bleached pulp yield and viscosity. As a result, the bleached pulp yield and viscosity increased by 2.1% and 10%, compared with fully bleached pulp at the end of the process, respectively, despite a decrease in ISO brightness.

Experimental process design for sorption capacity of Kogi and Ibusa clay activated with HNO<SUB align="right">3 and H<SUB align="right">2SO<SUB align="right">4 acids in palm oil bleaching

The palm oil bleaching process was optimised through characteristic study of the sorption capacity of Ibusa and Kogi clay activated with nitric and sulphuric acids. The raw clays were characterised for structure elucidation via FTIR and X-ray fluorescence spectroscopic techniques and the result indicates that Kogi clay is predominantly kaolinite while Ibusa sample is montmorillonite. The response surface methodology based on 42-full factorial design was applied for the process analysis. Effects of process variables such as acid concentration, bleaching temperature, contact time, clay-oil ratio and particle size distribution was analysed employing the characterisation-control-optimisation paradigm necessary for detailed process design for optimum bleaching efficiency. A sequence of experiments was carried out at different settings of the process variables and their interactive sorption effects were calculated in terms of adsorption efficiency. Acid concentration and bleaching time were found to be the most significant process parameter. Predictive equations describing the optimum bleaching efficiency in terms of the process variables were derived from regression analysis of the experimental data. A maximum mean adsorption strength of 40 units was predicted for both specimens through activation wit HNO3 acid at mean acid concentration of 6.12 mol/l and mean bleaching time of 48.88 mins, while H2SO4 acid recorded relatively low adsorption strength of 24 units with Kogi clay and negligible strength of 8 units with Ibusa sample at the same experimental condition. Overall, HNO3 acid activated Kogi clay shows robustness to expanded variable effects and could be recommended for general application in lieu of bentonite.

Pre-treatment of the paper pulp in the bleaching process using biodegradable chelating agents

The aim of this work was to study the application of two biodegradable chelating agents, pyridine-2,6-dicarboxylic acid (PDA) and methylglycinediacetic acid (MGDA), in the treatment of the pulp, prior to hydrogen peroxide bleaching. Such compounds must remove transition metals (Mn, Fe and Cu) from pulp, that catalyze the degradation of hydrogen peroxide, and Ca, which is also problematic due to the formation of precipitates that accumulate in the equipment. Computer simulations were first performed to study the best conditions for metal complexation, and optimum pH was defined as 5–5.5 for PDA and 6.5–7 for MGDA. Metals removal from the pulp, as well as the subsequent bleaching process (Q-P1-Paa-P2), were tested experimentally, and performances were compared to ethylenediaminetetracetic acid (EDTA). PDA removed both Mn and Ca efficiently, leaving most Mg in the pulp after first chelation stage, while MGDA had a lower Ca removal, even using a higher pH and concentration. Residual hydrogen peroxide and kappa number after peroxide stages showed a similar bleaching efficiency between the studied compounds and EDTA.

Application of ozone in cotton bleaching with multiple reuse of a water bath

This paper discusses the effect of ozone bleaching on the quality of cotton fabric in terms of whiteness, dye pick-up, copper number and degree of polymerization (DP). The process parameters (pH, ozone dose and treatment time) were optimized, and the best whiteness (60–62) and quality of bleached fabric was obtained at pH 5, 45 min treatment time and room temperature. A strongly acidic environment and longer ozonation time decreased the quality of fabric by producing a higher copper number (0.18) and DP loss (51.5%). Statistical analysis of the experimental data using analysis of variance confirmed that process parameters significantly affected the bleaching efficiency. The process was then applied to bleach 20 different samples of cotton fabric re-using the same water bath, and the whiteness of ozone-bleached samples did not decrease, even after the 20th reuse of the water bath.

Optimization of Color Pigments Removal from Palm Oil by Activated Ukpor Clay Using Response Surface Methodology

The aim of this study was to investigate the optimum operating process parameters during the adsorption of color pigments from palm oil onto activated Ukpor clay using Response Surface Methodology (RSM). The clay was activated using sulphuric acid solution. The process parameters investigated include; temperature, time, adsorbent dosage, adsorbent/oil ratio and stirring speed. The results showed that the bleaching efficiency was significantly affected by the linear, quadratic and some of the interaction terms. The optimum conditions derived via RSM were: temperature- 152.73 °C; time- 2.60 h; adsorbent dosage- 6.09 g; adsorbent/oil ratio- 0.05g/mL; stirring speed- 39.34rpm; and under these conditions the predicted bleaching efficiency was 82.67% which has good correlation with the experimental value of 82.25%. The high prognosis obtained in this study has shown that 5-level 5 factor fractional central composite design of the RSM is suitable for predicting the optimum adsorption conditions of color pigments from palm oil using activated Ukpor clay.

Cesium Salt of Sodium 30-Tungstopentaphosphate: An Effective and Green Polyoxometalate for Synthesis of Gold Nanoparticles along with Decoration of Titanium Dioxide with Gold Nanoparticles for Bleaching of Malachite Green

For the first time, capability of the cesium salt of sodium 30-tungstopentaphosphate, the so-called Preyssler’s anion (CsP5), as a green and eco-friendly polyoxometalate was investigated in the synthesis of gold nanoparticles and decoration of titanium dioxide with gold nanoparticles. Gold nanoparticles and nanocomposites were characterized by TEM, XRD, UV, and FTIR. TEM images showed that the gold nanoparticles have tubular and spherical shapes and particle size ranges from 10 to 25 nm. For gold-decorated titanium dioxide/Preyssler, a comparison between pure and amine-modified titanium dioxide showed higher loading of gold nanoparticles on amine-functionalized titanium dioxide. The performance of CsP5was compared with its pure acid (HP5). Our findings showed that CsP5, as a catalytic linker to bind onto titanium dioxide surface for reducing gold nanoparticles, renders decoration better than HP5in both pure and modified titanium dioxide. In addition, efficiency of the photocatalytic bleaching of malachite green by the synthesized nanocomposites was found to be excellent.

Effect of ultrasonic pre-treatment of thermomechanical pulp on hydrogen peroxide bleaching

Ultrasound pre-treatments of softwood TMP had been carried to evaluate its impact on the efficiency of hydrogen peroxide bleaching. The trials were performed after a factorial design of experiment using frequency, power and time as variables. The experiments were conducted in an ultrasonic bath and then bleached with hydrogen peroxide. Measurements such as brightness, L*A*B* color system coordinate, residual hydrogen peroxide and metal content were evaluated on bleached pulp. The results indicate that the effect of ultrasonic treatment on brightness was dependent on the ultrasound frequency used; the brightness increased slightly at 68 kHz and decreased at 40 and 170 kHz. These results were correlated to the ultrasound effect on the generation of transition metals (copper, iron and manganese) which are responsible for catalytic decomposition of hydrogen peroxide. The influence of metal interference was minimized by using a chelating agent such as diethylene triamine pentaacetic acid (DTPA). With the results obtained in this study we have identified a set of option conditions, e.g. 1000 W, 40 kHz, 1.5 % consistency and 0.2% addition of DTPA prior to the bleaching stage (after ultrasonic pre-treatment) who improve brightness by 2.5 %ISO.

Bleaching of eucalyptus kraft pulps with chlorine dioxide: Factors affecting the efficiency of the final D stage

We investigated the bleaching efficiency of the final chlorine dioxide (D2) stage in the D0(EP)D1D2 bleaching sequence, focusing on the effect of pH in relation to the bleaching history of pulp samples. The samples used were unbleached kraft Eucalyptus grandis pulps with kappa no. 14.8 and the same pulp oxygen-delignified to kappa nos. 12 and 9.8. The samples were bleached according to the D0(EP)D1 sequence to a brightness of about 86% ISO and then submitted to the final D2 stage under identical conditions (e.g., chlorine dioxide charge, time, temperature, and final pH). The target final brightness was 90.5% ISO. Changes in the kappa number, brightness, viscosity, and contents of hexenuronic acid, 4-O-methylglucuronic acid, and the total amount of carboxylic acid (COOH) groups in pulps were monitored during the bleaching sequence. The final brightness of eucalyptus kraft pulps increased when the terminal pH of the D2 stage was raised from 3.0 to 6.5. The 90.5% ISO target brightness in the D2 stage was achieved for all pulps within a pH range of 4.5–6.5, but this required adjusting final pH for individual samples. The optimal pH value with respect to pulp viscosity was between 3 and 5. Despite dissimilar conditions applied in previous bleaching stages, the samples after the D1 stage revealed similar residual lignin contents as shown by kappa number analysis. The content of hexenuronic acid in the samples, however, varied broadly, from 2 to 26 mmol/kg. Conductometric titration showed different amounts of carboxylic acid groups in pulps after the D1 stage, of which hexenuronic acid accounted for only a minor part. The variations in the fiber charge resulted from the different bleaching conditions applied before the D2 stage. The fiber charge affected the alkali demand in the final D2 stage, whereas variations in the alkali demand affected the initial pH and associated process kinetics. Lower total fiber charge was found to be beneficial for improved final brightening and viscosity when bleached at higher final pH.

An Approach to Industrial Application: Influence of Black Liquor and pH on Xylanase Efficiency in Bleaching of Eucalyptus Kraft Pulp

To obtain a more realistic appraisal of the potential efficiency of xylanases in the industrial bleaching, the influence of pH and the presence of black liquor (measured as COD) on the bleaching efficiency of two commercial xylanases was studied at high temperature. These pH’s, CODs, and temperatures are close to those used in the storage tower of the B fiber line in Jacareí unit of Fibria (Brazil). The pulp samples obtained after each bleaching stage were analyzed for kappa number, brightness, viscosity, and hexenuronic acid content, and so were the effluents for COD, TOC, color, turbidity, and pH after the enzymatic stage. On the basis of the results, the xylanases were found to increase pulp brightness in the treatment involving the most unfavorable conditions (viz. high COD and pH). However, an initial COD above 9 kgO2 t−1 and/or a pH higher than 9.5 detracted from their bleaching efficiency. The effect on the kappa number and hexenuronic acids content of the pulp was apparent immediately after the enzymatic stage, and the most marked increase in brightness was observed after the chlorine dioxide stage.

Impact of acid washing and chelation on Mg(OH)2-based hydrogen peroxide bleaching of mixed hardwoods CMP at high consistency

The removal of transition metal ions is crucial for improving the efficiency of subsequent peroxide bleaching. Acid-washing and chelation have been proposed for such a purpose. However, their influences on the Mg(OH)2-based peroxide bleaching of hardwood pulps at a high consistency have not been well documented in the literature. In this work, we studied the influence of acid-washing using sulfuric acid or chelation using diethylenetriaminepentaacetic (DTPA) on the Mg(OH)2- or NaOH-based hydrogen peroxide bleaching efficiency, effluent properties of bleaching filtrates, and paper properties. The results showed that for Mg(OH)2-based peroxide bleaching, the pulp yield and water retention value of acid-washed pulp were higher than those of the chelated pulp; the chemical oxygen demand (COD) and turbidity of the bleaching filtrates for the acid-washed pulp were lower than those of the chelated pulp. The bleached acid-washed pulp had lower strength properties than bleached chelated pulp did. Additionally, at a high pulp consistency (25%), the Mg(OH)2-based process had a higher bleaching efficiency and superior bleaching effluent properties, but a lower strength properties, in comparison with the NaOH-based process.

A Partial Magnesium Hydroxide Substitution for Sodium Hydroxide in Peroxide Bleaching of an Aspen CTMP

A partial substitution of sodium hydroxide (NaOH) by magnesium hydroxide (Mg(OH)2) as the alkali source was studied in peroxide bleaching of an aspen chemi-thermomechanical pulp (CTMP). The effects on pulp properties, including pulp strength, optical property and carboxylic groups content, and process characteristics, such as oxalate and anionic trash formation, were studied. The X–ray photoelectron spectroscopy (XPS) technique was used to determine the lignin and extractives concentrations on the fiber surface. With the increased Mg(OH)2 substitution ratio, the peroxide bleaching process gave a higher pulp yield and peroxide bleaching efficiency, produced pulps with higher light scattering coefficient and bulk, while the total oxalate, anionic trash, and chemical oxygen demand load (COD) were less. The total carboxylic groups content and the surface charge of pulp fibers were decreased. The underlying mechanism responsible for the decreased strength properties, when the Mg(OH)2 substitution ratio was increased, is discussed.

Study of Indigo carmine as radical probe in photocatalysis

The feasibility of using Indigo carmine (IC) as a probe of free radical production in photocatalysis was elucidated by comparative studies of its bleaching by γ radiolysis and TiO 2 photocatalysis. The γ radiation result from pH 3 to 10 shows that both OH and HO 2 can bleach IC and that the bleaching yields of OH is pH independent at ∼0.7 molecules per OH. The quantum yields ( ϕ) of OH from Degussa p25 TiO 2 photocatalysis from pH 3 to 10 was determined. It was found that ϕ was about 4% at pH 10 and dropped to below 1% at pH 3. This agrees well with the result of photocatalysis of Fricke dosimetry at pH 1. The effects of some common inorganic anions that may affect photocatalytic systems in technical applications (Cl −, SO 4 2−, Br −, HPO 4 2−, B 4O 7 2−, HCO 3 −/CO 3 2−) was also investigated, showing that these ions does not inhibit the photocatalytic bleaching efficiency of IC.

Polymer Composite with Three Electrochromic States

The electrochromic properties of an electrodeposited polymer composite consisting of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(3-methyl-2-{[3-(4-vinyl-benzyl)-3H-benzothiazol-2-ylidene]-hydrazono}-2,3-dihydro-benzothiazole-6-sulfonic) acid (polyABTS) are reported. Films of this polymer composite exhibit three electrochromic states in the visible region upon application of potentials at –800 mV, 0 V, and +800 mV versus Ag/AgCl, confirming that both polymers contribute to electrochromic switching. These films exhibit ultracontrasts between the bleached state at 0 V and the blue state at –800 mV (ΔT % = 33.6% at 615 nm) and the green state at +800 mV (ΔT % = 46.3% at 393 nm). The efficiency of cathodic coloration and bleaching of this material at 615 nm is 322.1 and 396.4 cm2 C−1, respectively, whereas the efficiency of anodic coloration and bleaching at 393 nm is 189.9 and 192.4 cm2 C−1, respectively. In comparison to previously reported films of polypyrrole (pPy) doped with the ABTS monomer (pPy[ABTS]), thick films of PEDOT[polyABTS] exhibit an increased stability to potential cycling both because PEDOT is more resistant to overoxidation than pPy and because polyABTS is a nonleachable dopant. Reversible redox behavior, anodic and cathodic coloration, fast response times, resistance to overoxidation, ease of fabrication, and low cost make this material competitive for electrochromic applications.

Evidence for Specificity in Lipid-Rhodopsin Interactions

The interaction of bovine rhodopsin with poly- and monounsaturated lipids was studied by (1)H MAS NMR with magnetization transfer from rhodopsin to lipid. Experiments were conducted on bovine rod outer segment (ROS) disks and on recombinant membranes containing lipids with polyunsaturated, docosahexaenoyl (DHA) chains. Poly- and monounsaturated lipids interact specifically with different sites on the rhodopsin surface. Rates of magnetization transfer from protein to DHA are lipid headgroup-dependent and increased in the sequence PC < PS < PE. Boundary lipids are in fast exchange with the lipid matrix on a time scale of milliseconds or shorter. All rhodopsin photointermediates transferred magnetization preferentially to DHA-containing lipids, but highest rates were observed for Meta-III rhodopsin. The experiments show clearly that the surface of rhodopsin has sites for specific interaction with lipids. Current theories of lipid-protein interaction do not account for such surface heterogeneity.

Inorganic Reactions in Chlorine Dioxide Bleaching of Softwood Kraft Pulp

A softwood kraft pulp (27 kappa) was bleached with chlorine dioxide to various end pH values. The formation of chlorite, chlorate, and chloride was measured to quantify the amount of chlorine dioxide wasted as a function of pH during a Do (pre‐bleaching) stage. Chlorate formation increased with a decrease in final pH. Conversely, residual chlorite increased with an increase in the final pH. After 120 min of bleaching the total residual chlorite and chlorate showed that no substantial increase in residual oxidant occurs when bleaching to an end pH below 3.4. As a result, the brightness and permanganate numbers for low pH chlorine dioxide bleached pulps did not differ when bleaching to an end pH between 3.4 and 1.8. However, decreasing the pH below 3.4 did result in increased organic chloride formation. The results are contrary to previous studies where the maximum bleaching efficiency for a D1 stage was reported to occur when the end pH was between 3 and 4.

Spectrophotometric and visual evaluation of vital tooth bleaching employing different carbamide peroxide concentrations

Objective The aim of the present study was to assess the hypothesis that the efficiency of vital tooth bleaching depends on the concentration of carbamide peroxide agents. Methods The front teeth of 30 subjects were bleached at home with 10%, 17% or 0% (control) carbamide peroxide for 1 week in a double-blind study design. Tooth shades were determined in the LCH color space employing a visual shade matching system and a spectrophotometer. Differences in lightness (Δ l), chroma (Δ c) and hue (Δ h) were measured to assess the treatment process. After 2 weeks of no treatment, tooth shades were evaluated again to assess stability of the resultant shade. Results First-time changes of shade values could be observed after 3 days in the 17% group and after 7 days in the 10% group. After 1 week, in both the 17% group (Δ l: 2.80, Δ c: −3.33, Δ h: 0.60) and the 10% group (Δ l: 2.61, Δ c: −2.54, Δ h: 0.09), values for lightness and chroma were significantly different from the control (Δ l: 0.13, Δ c: 0.14, Δ h: 0.21, p < 0.05) with no difference between the test groups ( p > 0.05). Two weeks after treatment, a rebound of shade values could be observed in the test groups ( p < 0.05). Significance The study indicates that higher concentration bleaching agents might whiten teeth faster with major changes in lightness and chroma. However, by bleaching daily for 1 week, similar effects can be achieved with both a high and a low concentration agent. After treatment, a regression of the resultant shade has to be expected.

Determination of Al(III) activation conditions for white bentonite used for cottonseed oil bleaching by robust design

AbstractThe optimum Al(III) activation conditions for white bentonite (Ordu, Turkey), used as a bleaching agent for cottonseed oil, were investigated. AlCl3–clay suspension was hydrolyzed in situ using NaOH to investigate possible pillars. Five controllable factors that mainly affect the activation process were specified as initial AlCl3 concentration (F1), OH−/Al3+ molar ratio (F2), NaOH volumetric flow‐rate (F3), cation‐exchange temperature (F4) and thermal treatment temperature (F5). Each factor was examined at four levels by using a robust (Taguchi) design to determine optimum activation conditions. The response variable of each experimental run was taken as bleaching efficiency, which is defined in terms of absorbance at 420 nm. The effect of desired levels of factors to the system response was compared using the signal‐to‐noise (S/N) ratio. An importance factor (IF) was suggested in order to compare the affectability of each factor to the response variable by using the integrated area under the S/N ratio curves. The most important factor affecting bleaching efficiency was F5, followed in sequence by F2 &gt; F1 &gt; F4 &gt; F3. The availability of AlO species after activation in the clay crystal structure was determined by FTIR analysis. The optimum levels of each factor for Al3+ activation of clay were F1 5 meq g−1 clay, F2 2.0, F3 1200 mL h−1, F4 25 °C and F5 700 °C. Copyright © 2005 Society of Chemical Industry

Application of xylanase enzyme of Bacillus coagulans as a prebleaching agent on non-woody pulps

The effectiveness of xylanase as a prebleaching agent has been established on a commercial scale. The efficiency of bleaching improves with the enzyme treatment but it varies with the pulping method and pulp raw material. In the present work, crude xylanase from Bacillus coagulans has been characterized with respect to the operational parameters and the stabilities at various pH values. Xylanase from B. coagulans has been tested on three non-woody pulps as a prebleaching agent. The effects of crude enzyme on wheat straw, rice straw and jute pulps at two different initial pH of pulp have been studied and a maximum brightness gain of 5.1 points has been achieved with rice straw pulp at an initial pH value of 8.5. In the case of wheat straw and rice straw pulps, maximum brightness gain has been obtained at the higher pH values.

Efeito do conteúdo e da natureza da lignina residual na eficiência e na seletividade do branqueamento com ozônio

Neste estudo foram avaliados os efeitos do conteúdo e da natureza da lignina residual na eficiência e na seletividade do branqueamento com ozônio de polpa kraft convencional (kraft) e pré-deslignificada com oxigênio (kraft-O). Constatou-se que a eficiência do branqueamento com ozônio se eleva com o aumento do conteúdo de lignina residual da polpa. O tratamento com ozônio é mais seletivo para polpas kraft-O, mas para um mesmo tipo de polpa a seletividade de branqueamento com ozônio se eleva com o aumento de lignina residual. A eficiência do branqueamento com ozônio aumenta com o teor de lignina fenólica na polpa, entretanto a seletividade é negativamente afetada pela presença destas estruturas.