Bleaching Parameters Research Articles

The issue of laboratory bleaching in the infrared-radiofluorescence dating method

Measuring the infrared radiofluorescence (IR-RF) signal is methodologically simpler than measuring the IRSL or TL signals. However, unlike classical luminescence measurements, the IR-RF signal is totally resetting when its highest value is reached. Previous studies (Buylaert et al., 2012; Trautmann et al., 2000) reported that the proper bleaching level of an IR-RF signal is difficult to define and seems to be dependent 1) on the wavelength used for bleaching and 2) on exposure duration. The IR-RF signals from K-feldspar samples have been measured with various bleaching wavelengths and exposure time using a Lexsyg research luminescence unit. In this study, we propose suitable bleaching parameters adapted to IR-RF measurements.

Experimental investigation of processing parameters and effects of degumming, neutralization and bleaching on lampante virgin olive oil's quality

The refining of crude oil is a purification process which aims to yield a high amount of triglycerides and to produce an acceptable refined oil quality. This work focuses on two topics: (1) the comparison of adsorption performance of four clays having different activation levels (Ads1, Ads2, Ads3, and Ads4) and (2) the identification of the effective factors using a fractional factorial design method of lampante virgin olive oil refining processes involving degumming, neutralization, and bleaching. The effects of the phosphoric acid concentration, ratio (acid/oil), degumming contact time, neutralizing agent excess, earth clay dosage, contact time and temperature of bleaching step were investigated through the determination of residual phospholipids content, free fatty acid percentage, oxidative stability, color, and trans fatty acids content.Based on adsorption isotherms, Ads1 is selected as the adequate clay contributing to color reduction with low formation of oxidation products. The results of a 2III7−4 model showed that the strength and the amount of phosphoric acid, and the bleaching parameters were the principal factors that controlled bleached oil quality. Residual phospholipids and acidity decreased as degumming agent increased. Additionally, the bleaching parameters were found to significantly affect the lovibond scale and oxidative stability.

Re-evaluating luminescence burial doses and bleaching of fluvial deposits using Bayesian computational statistics

Abstract. The optically stimulated luminescence (OSL) signal from fluvial sediment often contains a remnant from the previous deposition cycle, leading to a partially bleached equivalent-dose distribution. Although identification of the burial dose is of primary concern, the degree of bleaching could potentially provide insights into sediment transport processes. However, comparison of bleaching between samples is complicated by sample-to-sample variation in aliquot size and luminescence sensitivity. Here we begin development of an age model to account for these effects. With measurement data from multi-grain aliquots, we use Bayesian computational statistics to estimate the burial dose and bleaching parameters of the single-grain dose distribution. We apply the model to 46 samples taken from fluvial sediment of Rhine branches in the Netherlands, and compare the results with environmental predictor variables (depositional environment, texture, sample depth, depth relative to mean water level, dose rate). Although obvious correlations with predictor variables are absent, there is some suggestion that the best-bleached samples are found close to the modern mean water level, and that the extent of bleaching has changed over the recent past. We hypothesise that sediment deposited near the transition of channel to overbank deposits receives the most sunlight exposure, due to local reworking after deposition. However, nearly all samples are inferred to have at least some well-bleached grains, suggesting that bleaching also occurs during fluvial transport.

An environmentally safe and nondestructive process for bleaching birch veneer with peracetic acid

The industrial production of dyed wood veneers is increasing significantly. The bleaching process prior to dyeing is a key step. An effective and nondestructive process was developed in this work for bleaching the birch veneer by peracetic acid. The effects of bleaching parameters, such as whiteness increase, weight lose rate, dimensional stability and surface wettability were investigated, as well as a comparison of different bleaching processes with hydrogen peroxide and sodium hypochlorite as bleaching agents. Fourier transform infrared spectrum and Scanning electron microscope were used to characterize the bleached veneers. The obtained bleaching conditions are as follows: peracetic acid 10 g/L, sodium pyrophosphate 0.4 g/L, pH 6.5, material to liquor ratio 1:20, at 65 °C for 1 h. The whiteness increase from peracetic acid bleaching is a little lower than that of hydrogen peroxide bleaching, but far higher than that of sodium hypochlorite bleaching. The weight lose rate of veneers bleached with peracetic acid is only 1.74%, far lower than those with hydrogen peroxide and sodium hypochlorite. And the dimensional change sequence is peracetic acid <hydrogen peroxide <sodium hypochlorite. The initial contact angle of unbleached veneer is 82°. After bleached by peracetic acid, hydrogen peroxide and sodium hypochlorite, the initial contact angle changed to 81°, 65° and 56°, respectively. Fourier transform infrared spectrum and Scanning electron microscope results show that weakly acidic peracetic acid bleaching had no obvious impact on wood structure, however, the alkaline hydrogen peroxide and sodium hypochlorite bleaching indeed removed some lignin from the surface of the veneer. Peracetic acid bleaching is advantageous for wood and is a promise method for commercial production. The present work can help to make technical innovations in wood bleaching process.

Determining fluvial sediment virtual velocity on the Mojave River using K-feldspar IRSL: Initial assessment

The Mojave River of Southern California was chosen as a field site to investigate the applicability of luminescence dating to sediment transport rate problems. Grains in the active channel of the river are expected to show signs of partial bleaching and this makes it difficult to determine time since deposition accurately. A modification of the multiple elevated temperature post-IR IRSL (METpIRIR) procedure, (Buylaert et al., 2009; Li and Li, 2011), was used for K-feldspar grains (175–200 μm) at temperature increments of 50, 95, 140, 185, and 230 °C in order to provide more information about relative signal bleaching among samples. The measurements show an exponential decrease in equivalent dose (De) with distance down the Mojave River. Higher temperature pIRIR signals are bleached more slowly than lower temperature ones (Buylaert et al., 2009). The De for samples at 50 °C is roughly constant along the river. These results suggest cyclical bleaching and burial as grains are transported downriver and higher energy (deeper) traps are vacated. The pattern of De values for the Mojave River can be used to constrain the sediment transport rate for this river by building a model of growth and bleach for each temperature increment. A bleaching experiment was run with multiple aliquot samples for direct sunlight exposure times of 0, 10, 30, 300, 1000, 3000, 10,000, and 30,000 s. The MET-pIRIR procedure was applied at each temperature increment for each exposure time aliquot and the results for all exposure times were fit to the general order kinetics equation using a non-linear regression. The bleaching parameters were used in conjunction with the SAR growth curves to build a model of partial bleaching of grains during transport that is fitted with a χ2 test to the pIRIR data from the Mojave River. This model is not a unique solution, but can be used to assess the likelihood of various sediment transport regimes.

Clay Characterization and Optimisation of Bleaching Parameters for Palm Kernel Oil Using Alkaline Activated Clays

The optimum bleaching parameters (clay dose and bleaching time) for palm kernel oil were determined using alkaline activated clay locally sourced in Nigerian. Activation was carried out using NaOH and KOH. The raw and activated clay samples were characterized using XRD and XRF. Bleached oil was analyzed for % colour reduction (%CR) and percentage free fatty acid (FFA) content before and after bleaching. Alkaline activation resulted to total dissolution of Mg2+ and Ca2+ ions in the octahedral sheet. The activation also affected the tetrahedral sheet by reducing the % composition of the silica and alumina ion after the modification. The results showed that alkaline activation had significant effect on mineralogical and chemical composition of the clay samples. The optimum bleaching conditions (clay dosage and bleaching time) of 3%/weight of oil and 30 mins resulted in 33.3% CR and %FFA of 2.2. It was discovered that NaOH activated clay resulted to higher %CR while KOH activated clay shows affinity for reduced %FFA but at higher concentration of 5 M. This research has further established that alkaline activated clays are feasible alternative for acid activated clays in vegetable oil bleaching.

The Influence of Bleaching Agent and Temperature on Bleaching Efficacy and Volatile Components of Fluid Whey and Whey Retentate

Fluid whey or retentate are often bleached to remove residual annatto Cheddar cheese colorant, and this process causes off-flavors in dried whey proteins. This study determined the impact of temperature and bleaching agent on bleaching efficacy and volatile components in fluid whey and fluid whey retentate. Freshly manufactured liquid whey (6.7% solids) or concentrated whey protein (retentate) (12% solids, 80% protein) were bleached using benzoyl peroxide (BP) at 100 mg/kg (w/w) or hydrogen peroxide (HP) at 250 mg/kg (w/w) at 5 °C for 16 h or 50 °CC for 1 h. Unbleached controls were subjected to a similar temperature profile. The experiment was replicated three times. Annatto destruction (bleaching efficacy) among treatments was compared, and volatile compounds were extracted and separated using solid phase microextraction gas chromatography mass spectrometry (SPME GC-MS). Bleaching efficacy of BP was higher than HP (P < 0.05) for fluid whey at both 5 and 50 °C. HP bleaching efficacy was increased in retentate compared to liquid whey (P < 0.05). In whey retentate, there was no difference between bleaching with HP or BP at 50 or 5 °C (P > 0.05). Retentate bleached with HP at either temperature had higher relative abundances of pentanal, hexanal, heptanal, and octanal than BP bleached retentate (P < 0.05). Liquid wheys generally had lower concentrations of selected volatiles compared to retentates. These results suggest that the highest bleaching efficacy (within the parameters evaluated) in liquid whey is achieved using BP at 5 or 50 °C and at 50 °C with HP or BP in whey protein retentate.

Sample pretreatment for oxalate analysis and the effect of peroxide bleaching parameters on oxalate formation

Sample pretreatment for oxalate analysis and the effect of peroxide bleaching parameters on oxalate formation

Hydrogen peroxide bleaching of hardwood kraft pulp with adsorbed birch xylan and its effect on paper properties

The adsorption of xylan on pulp fibers improves the strength properties of paper. However, the optical properties are decreased significantly. The objective of our research was to bleach hardwood kraft pulp with adsorbed birch xylan by hydrogen peroxide and study the effect of bleaching parameters on paper properties. The bleaching parameters studied included bleaching temperature, time, initial pH as well as MgSO4 dosage. The optical properties (whiteness, brightness, opacity) and physical properties (tensile index, tearing index, bulk) of handsheets made from the pulp bleached with different process variables were measured. The results showed that better optical properties were obtained with higher bleaching temperature, longer bleaching time, and more MgSO4 dosage. Bleaching from an initial pH of 11 provided the highest brightness value. On the other hand, strength properties were improved with decreasing of the bleaching temperature, and increasing the initial pH and MgSO4 dosage. The relationship between strength properties and bleaching time varied depending on bleaching temperature. According to the results, both good mechanical properties and optical properties could be achieved when the operating parameters were controlled properly. Therefore hydrogen peroxide bleaching was proved to be a suitable method for bleaching hardwood kraft pulp with adsorption of birch xylan.

Cold pad–batch bleaching of cotton fabrics with a TAED/H2O2 activating system

The cold pad–batch bleaching of cotton fabrics using a tetra acetyl ethylene diamine/hydrogen peroxide (TAED/H2O2) activating system is investigated in this study. The effects of key bleaching parameters (hydrogen peroxide dosage, sodium hydroxide dosage, TAED/H2O2 mol ratio and batch time) on the bleaching efficiency were investigated by single‐factor analysis and orthogonal experiment analysis. The performance of the activator TAED in the cold pad–batch process was examined and the activating mechanism is discussed. The optimised bleaching recipe and processing conditions are reported, and the optimal activated bleaching process is also compared with a conventional cold pad–batch bleaching process. The results show that the optimised TAED/H2O2 activated bleaching system could achieve high quality cotton bleaching with comparable fabric whiteness to the conventional system at much shorter batch times, and with significantly reduced fabric strength loss and decreased alkali consumption, which would be beneficial to sustained development of the textile wet‐processing industry.

Photochromism and Thermochromism of some Spirooxazines and Naphthopyrans in the Solid State and in Polymeric Film

In this work the photochromic behaviors of four Reversacol compounds from James Robinson Ltd., previously investigated in solution, have been studied in a microcrystalline solid phase and embedded in a poly(methyl methacrylate) matrix (PMMA). The compounds studied belong to the classes of spirooxazines and naphthopyrans. In solution, they showed photocoloration and thermocoloration. Embedded into polymeric films, as well as in the microcrystalline phase, they have maintained their photochromic and thermochromic behavior. The photocoloration quantum yields in PMMA were determined and found to be fairly high. Compared to solution, the kinetic and thermodynamic activation parameters of thermal bleaching significantly changed. The solid environment has the effect of slowing down the bleaching rates in films as well in the pure crystalline phase and introduces multiexponential terms in the photocoloration and thermal bleaching kinetics. Activation enthalpy and entropy decrease, compared to solution, leaving the activation free energy substantially unchanged. Thermochromism was characterized through the equilibrium constant and the thermodynamic standard parameters, ΔH0, ΔS0, and ΔG0, of the thermal reactions. Time-dependent processes were also analyzed according to the maximum entropy method (MEM). Based on the data from the least-squares and MEM treatments, the occurrence of multiexponential kinetics in polymers was attributed to the effects of the inhomogeneous distribution of free volume in the matrix.

TL, EPR and optical absorption in natural grossular crystal

Grossular is one of six members of silicate Garnet group. Two samples GI and GII have been investigated concerning their luminescence thermally stimulated (TL). EPR and optical absorption and the measurements were carried out to find out whether or not same point defects are responsible for all three properties. Although X-rays diffraction analysis has shown that both GI and GII have practically the same crystal structure of a standard grossular crystal, they presented different behavior in many aspects. The TL glow curve shape, TL response to radiation dose, the effect of annealing at high temperatures before irradiation, the dependence of UV bleaching parameters on peak temperature, all of them differ going from GI to GII. The EPR signals around g=2.0 as well as at g=4.3 and 6.0 have much larger intensity in GI than in GII. Very high temperature (>800 °C) annealing causes large increase in the bulk background absorption in GI, however, only very little in GII. In the cases of EPR and optical absorption, the difference in their behavior can be attributed to Fe 3+ ions; however, in the TL case one cannot and the cause was not found as yet.

Photochromic, Thermochromic, and Fluorescent Spirooxazines and Naphthopyrans: A Spectrokinetic and Thermodynamic Study

The photochromic and thermochromic behavior of four commercially available Reversacol dyes are presented. The compounds studied belong to the class of spirooxazines and naphthopyrans, which are typically thermoreversible photochromic molecules. On stimulation with UV light, these compounds become colored and exhibit spectra which extend over the whole visible region. Increasing the temperature causes spontaneous coloration (thermochromism). Herein, absorption and fluorescence spectra, molar absorption coefficients of the colorless and colored forms, fluorescence and photochemical quantum yields, and kinetic parameters of thermal bleaching (rate constant, frequency factor, and activation energy) are determined in acetonitrile solution. The thermal ground-state reaction is exhaustively described in terms of thermodynamic parameters (equilibrium constant, free energy, enthalpy, and entropy). Temperature effects on photochemical and thermal colorabilities are evaluated. The results indicate that the two spirooxazines are good photochromes below room temperature, whereas they are efficient thermochromic compounds above room temperature. Naphthopyrans are better photochromes but worse thermochromic compounds than spirooxazines.

The Effect of Tb and Sm Ions on the Photochromic Behavior of Two Spiropyrans of Benzoxazine Series in Solution

The photochromism of [7′-hydroxy-8′-formyl-3-methyl-4-oxospiro[1,3-benzoxazin-2,2′-[2H-1]benzopyran],SP(I),[7′-hydroxy-8′-formyl-3-benzyl-4-oxospiro[1,3-benzoxazin-2,2′-[2H-1]benzopyran] SP(II) and their coordination with Tb3+and Sm3+ ions have been studied in DMF. UV/vis induced-color development due to heterolytic bond cleavage of SP(I) and SP(II) is greatly influenced by complexation with the lanthanide ions. The irradiation-induced color enhancement due to ring opening and thermal decoloration of the open forms of SP(I), SP(II) follows first-order kinetics. Physical characteristics of the studied systems such as colorability and relaxation time of thermal bleaching parameters were determined. Moreover, light-energy transfer-induced luminescence of lanthanide ions via coordination with the two spirobenzoxazines was monitored.

Strategies to reduce the brightness reversion of industrial ECF bleached Eucalyptus globulus kraft pulp

AbstractBACKGROUND: Brightness stability is a key property of bleached chemical pulps and is primarily determined by wood species and bleaching process conditions. Eucalyptus globulus is becoming a very important raw material for hardwood pulp production. In spite of this importance, there is a relative lack of systematic studies in the literature dealing with the subject. This research aims to study the effect of some of the foremost bleaching parameters of a DEDD bleaching sequence as well as the effect of a final P stage (DEDP instead of DEDD) in the brightness stability of bleached E. globulus kraft pulps.RESULTS: The increase of the D0 stage temperature from 55 °C to 90 °C caused an increase in brightness stability. Increasing the ClO2 charges from 2.8% to 3.2% also improved significantly the brightness stability. A high H2SO4 charge in the D0 stage (10 kg tonne−1 pulp) diminished the brightness stability. The combination of H2O2 addition to the E stage and ClO2 reduction in the two final D stages does not affect brightness reversion. Raising the D2 stage temperature from 65 °C to 82 °C decreased the brightness reversion, while an increase was obtained when the temperature rose above 82 °C. Substitution of the last ClO2 stage in the DEDD sequence by a H2O2 stage (DEDP) significantly reduced the brightness reversion.CONCLUSION: For an existing pulp mill in which the implementation of new technologies to improve brightness reversion is considered, the results obtained showed that brightness stability can be improved without any significant capital investment. Copyright © 2007 Society of Chemical Industry

Photochromic behaviour of Berry Red studied in solution and polymer films

In this work, the photokinetic study of Reversacol Berry Red (2,2-bis(4-methoxyphenyl)-5,6-dimethyl-2H-naphtho[1,2-b]pyran), a photochromic compound from James Robinson Ltd., has been carried out in solution and in polymeric films (Paraloid B-72 and Polyvinyl butyral) in order to quantitatively characterize its photochromic properties by means of objective parameters in different environments. In solution, Berry Red shows reversible and intense photocolouration at room temperature and significant solvatochromic effect in the spectrum of the coloured form. Embedded into polymeric films, Berry Red maintains its thermally reversible photochromic behaviour. However, the photocolouration quantum yield is appreciably reduced and the kinetic parameters of bleaching are significantly altered. The matrix has the effect of lowering both the activation energy (up to a half of the value in solution) and the pre-exponential factor of thermal bleaching (by about seven orders of magnitude). These compensating effects make the bleaching rates in films close to that in solution. The negative values of activation entropy determined in polymer films are related to the rearrangement of the molecule into the activated complex structure.

Bleaching of Kenaf and Cornhusk Fibers

Kenaf and cornhusk fibers have been bleached to CIE whiteness indexes of 66 and 74, respectively, without using any optical brighteners. A delignification process prior to bleaching has been used to partially remove the lignin from the fibers without affecting other fiber properties. Bleaching variables such as the concentration of hydrogen peroxide, time, temperature, and pH have been optimized for both the kenaf and cornhusk fibers. The effects of various bleaching parameters on the whiteness index and the breaking tenacity of the fibers have been reported. The whiteness of kenaf fibers reported here is high compared to the whiteness achieved by other bleaching processes developed earlier.

Photoinduced Processes in Dipyrrolyl‐Perfluoro‐Cyclopentenes

The photobehavior of five photochromic dipyrrolyl-perfluoro-cyclopentenes was studied by steady state and time-resolved absorption spectroscopy. The quantum yields of the UV-photoinduced ring-closing reaction (coloration) and the visible-stimulated cycloreversion reaction (bleaching) were measured. Kinetic and thermodynamic parameters of thermal bleaching were also determined. Nanosecond time-resolved experiments showed formation of a transient, which was not a precursor of the reaction photoproduct. This transient was tentatively assigned to a radical cation formed by direct photoionization through a short-lived triplet state. The nature of the transient species was supported by photoinduced electron transfer to electron acceptors.

Statistical modelling of single grain quartz De distributions and an assessment of procedures for estimating burial dose

It is possible to increase the accuracy of the optical dating of some Quaternary deposits by deriving age estimates from individual quartz grains. Age estimates from individual grains within single samples display varying degrees of inconsistency however and this paper address the difficulties in reducing complex distributions of single-grain age estimates to single accurate sample ages using existing statistical age models. A modelled response of the quartz OSL signal to irradiation and illumination (both in the laboratory and under natural conditions) was used to test the accuracy of various published statistical age-models. ‘Aeolian’ and ‘fluvial’ transport conditions were simulated by adjusting the wavelength range of the daylight spectrum and the incident photon flux during the simulated bleaching event. A heterogeneous mix of grains was produced using a Monte Carlo approach, in which key irradiation and bleaching parameters were varied for each simulated grain, and the accuracy of published statistical models assessed. Results suggest that no single age-model is appropriate for all modelled cases. A formal decision process is suggested and shown to make appropriate choices between the available age-models in each of the modelled cases and in ∼85% of cases using 43 known-age sediment samples.

Evaluating Hydrogen Peroxide Bleaching with Cationic Bleach Activators in a Cold Pad-Batch Process

Bleach activators generate peracids in the presence of hydrogen peroxide and alkali that are more potent oxidizing agents than hydrogen peroxide under comparable bleaching conditions. The effects of key bleaching parameters (activator concentration, hydrogen peroxide, chelant, and pH) on the performance of cold pad-batch bleaching on cotton are investigated. Optimized recipes are determined for two cationic activators, N-[4-(triethylammoniomethyl) benzyl]ca prolactam chloride and 6-( N,N,N-trimethylammonio) hexanoyl caprolactam p-toluenesulfo nate, using a central composite experimental design. The laboratory optimized conditions are used for pilot plant scale bleaching of cotton knit fabric. CIE whiteness index values are calculated from measured reflectance data of the pilot scale bleaching and are in close agreement with those predicted by the experiment. A high level of whiteness ( CIE WI &gt; 70) is achieved for both activators with 8-hour batching, and measurements of the degree of polymerization of the bleached and greige fabrics show little fiber damage in each case.