The effect of cold-light-activated bleaching treatment on enamel surfaces in vitro

This in vitrostudy aims to evaluate the crystal and surface microstructure of dental enamel after cold-light bleaching treatment. Twelve sound human premolars were cross-split into four specimens, namely, mesio-buccal （Group LP）, disto-buccal （Group P）, mesio-lingual （Group NP） and disto-lingual （Group L） specimens. These four groups were treated using the standard cold-light bleaching procedure, a bleaching agent, a peroxide-free bleaching agent and cold-light, respectively. Before and after treatment, all specimens were analyzed by high-resolution, micro-area X-ray diffraction and scanning electron microscopy. Using a spectrometer, tooth color of all specimens was measured before and after treatment. The phase of the enamel crystals was identified as hydroxyapatite and carbonated hydroxyapatite. After treatment, specimens in Groups LP and P showed significantly weaker X-ray diffraction peaks, significant reduction in crystal size and crystallinity, significant increase in L~ but decrease in a＊ and b＊, and obvious alterations in the surface morphology. However, specimens in Groups NP and L did not show any significant changes. The cold-light bleaching treatment leads to demineralization in the enamel surface. The acidic peroxide-containing bleaching agent was the major cause of demineralization, whereas cold-light did not exhibit significant increase or decrease effect on this demineralization.

Characterization, Acid Activation and Bleaching Performance of Bentonite from Xinjiang

Bentonite produced in Xiazijie, Xinjiang (China) was characterized by X-ray diffraction (XRD), dif- ferential thermal analysis (DTA), thermogravimetric analysis (TG) and cation exchange capacity (CEC). The ben- tonite is composed of dioctahedral montmorillonite with predominant quantity, certain amounts of quartz, feldspar and illite and minor amounts of kaolinite, gypsum, etc. The raw bentonite has a CEC of 0.6497 meq·g-1 and allows to be characterized as typical sodium bentonite. In order to bleach cottonseed oil, optimum conditions for sulfuric acid activation of the raw bentonites were investigated, which were obtained by selecting various acid strength, at 96—98℃ and activating for 4h with 1︰2 solid-liquid ratio. The acid activation bentonites were suitable for decol- orization of cottonseed oil through removing carotene and chlorophyll. The bleaching capabilities of different pig- ments with activated bentonite with treatment of 25% sulfuric acid were 70.3%, 73.1%, 83.2%, 81.8% and 88.9%, respectively. Bleaching with acid activated bentonite gave oils lower peroxide values and acid values.

The Numerical Simulation of the Flow Field in a Cold Model of Five-stage Cyclone Preheater and Precalciner System

The flow field in a cold model of 2500 t/d five-stage cyclone preheater and precalciner system was numerically simulated. Renault stress model (RSM) turbulent model was adopted to simulate the flow field, and a hybrid mesh scheme was selected to generate calculation mesh. With the first order upwind difference, finite-volume method was used to convert turbulent equations into difference equations pressure-velocity coupling which were solved by the classic simple algorithm, and during the course of numerical solution, mesh self-adapting technology was applied. The main flow field structures of the whole system and each part of the cold model were studied by analyzing the simulation results.

Recovery of oil and free fatty acids from spent bleaching earth using sub-critical water technology supported with kinetic and thermodynamic study

This work represents the extraction of oil with high free fatty acid content from spent bleaching earth using sub-critical water technology as a greener production pathway. The extraction efficiencies under different conditions were investigated. The studied parameters include temperatures in the range of 180 to 270°C, the feed to solventfeed-to-solvent (in this case water) ratio (1:1, 1:2, 1:3, 1:4 and 1:5) and extraction times in the range of 5-60 minutes. The results showed that the optimum temperature, feed to solventfeed-to-solvent ratio, and extraction time were 270°C, 1:3, and 20 minutes, respectively. In another experiment, the extracted free fatty acids were converted into mono-, di-, and triglycerides through esterification with glycerol to increase the value added of the extracted products. The kinetics of the extraction process was found to be corresponding to an irreversible consecutive unimolecular-type first order reaction, consisting of the extraction step followed by the decomposition reaction step. Both reaction rates of extraction and decomposition were estimated using the reaction rate equations utilizing the nonlinear regression method. The apparent activation energy was calculated to be 46.1 kJ·mol-1. This result indicates a diffusion controlled reaction. For more exploration and deep understanding of the extraction mechanism, other thermodynamic parameters were also calculated and analyzed including,ΔH#, ΔS#, and ΔG# of the extraction step.

Adsorption Behavior of Acid-Leached Clays in Bleaching of Oil

The available data have shown that acid-leached clays had sites for adsorption of impurities in oils. Data obtained on residual impurities in cotton and sunflower-seed oils bleached with the same clay materials produced linear Langmuir and Freundlich isotherms. The increase in constant, k with increase in both temperature of thermal activation and concentration of acid used to leach the clay, suggests that bleaching efficiency increased. The value of n decreased with increase in temperature of activation and concentration of acid used to leach the clay suggesting that bleaching capacity increased. The mineral compositions of the clays influenced their surface, structural and bleaching properties.

Bleaching of Black Human Hair

Bleaching of black human hair has been studied systematically. On the basis of experimental data the technology of human hair bleaching through five processes was established. The optimum technology of improving the whiteness and reducing damage on fibers has been found. The technology can provide good luster,smooth handle and relatively high strength retention to human hair used for wigs or drama articles, meeting the needs of people better. Moreover, it also has important reference value to bleaching of other colored fibers.

Five-Stage Model of the Palaeozoic Crustal Evolution in Xinjiang

Abstract: The great majority of the Palaeozoic orogenic belts of Central Asia are of the intercontinental type, whose evolution always follows a five-stage model, i.e. the basal continental crust-extensional transitional crust-oceanic crust-convergent transitional crust-new continental crust model. The stage for the extensional transitional crust is a pretty long, independent and inevitable phase. The dismembering mechanism of the basal continental crust becoming an extensional continental crust is delineated by the simple shear model put forward by Wernike (1981). The continental margins on the sides of a gently dipping detachment zone and moving along it are asymmetric: one side is of the nonmagmatic type and the other of the magmatic type with a typical bimodal volcanic formation. In the latter case, however, they were often confused with island arcs. This paper discusses the five-stage process of the crustal evolution of some typical orogenic belts in Xinjiang.

Effects of Mg-based Alkaline Peroxide Bleaching on Physical Properties of Poplar Bleached Chemi-thermomechanical Pulp and Its Influence Mechanism

In this study,Mg O was partially used as an alkali source in the peroxide bleaching process of bleached chemi-thermomechanical pulp(BCTMP).The effects of substitution percentage of Mg O for Na OH on the bulk,optical,and physical properties of bleached pulp,and the main effluent characteristics were analyzed.In addition,the influencing mechanism of Mgbased alkali on the strength properties of the BCTMP was further investigated.Strength properties of the BCTMPs were investigated as a function of charge characteristics,fiber morphology,surface lignin content,relative bonding area,and hydrogen bonds of the BCTMP.The results showed that cationic demand(CD) and chemical oxygen demand(COD_(Cr)) of the bleaching effluent decreased as the substitution percentage of Mg O for Na OH increased; meanwhile,the bulk and optical properties of the BCTMP increased.Nevertheless,the strength properties(tensile,tear,and burst indices) of the bleached pulp decreased as the substitution percentage of Mg O for Na OH increased.The decrease in the fiber charge density and increase in the surface lignin content affected the fiber swelling,resulting in a decline in pulp interfibers bonding strength and further loss of the tensile and burst indices.

Tentative Research of Short Process of Jute Degumming and Bleaching

The feasibility of combination process of jute degumming and bleaching with alkali-hydrogen peroxide in one-step-one-bath was discussed. The combination process basically has the similar function as the traditional two-step-two-bath method. The factors such as hydrogen peroxide concentration, CBI concentration, sodium hydroxide concentration, treatment time and temperature were studied respectively, and then an orthogonal experiment was designed to study the interactions among the hydrogen peroxide concentration, CBI concentration, sodium hydroxide concentration. After the designed experiments, the optimum treatment conditions were obtained as follows: hydrogen peroxide of 12g/L, sodium hydroxide of 4g/L, CBI of 4g/L, JFC of 1g/L, treatment time of 60min and temperature of 75℃.

Fabrication of Polymer Nonlinear Directional Coupler by Photo-bleaching

The preparation of a nonlinear directional coupler in polymer PMMA/DR1 film by photobleaching is studied. We find it easier to obtain a required coupling length by controlling photo bleaching time than by controlling the dimension of the coupler. The transmittance of each arm is measured when the pulse input light energy changes in our experiment. The experimental results show that the coupling length will change with the intensity of input light due to optical nonlinearities of the polymer PMMA/DR1 at 1 064 nm.

APPLICATIONS OF FLOCCULANT IN BLEACHING AND WASHING OF KAOLIN

The difficulties of washing during the dressing of kaolin ore have been analyzed, the multistep intermittent washing model has been deduced, and effective methods for dealing with the difficulties were put forward. Experimental results show that the bleaching and washing process was enhanced, the washing time was shortened and the consumption of water was reduced by means of adding flocculant.

FT-IR Microspectroscopic Imaging of Cross-Sectioned Human Hair during a Bleaching Process

We investigated bleached human hair by FT-IR microspectroscopy and chemical imaging. The cross sectioned hair is approximately 90 μm in diameter, showed cuticle and cortex in chemical imaging. Differential amide I/II absorbance ratio and broadening amide I band between in the cortex and cuticle were confirmed in FT-IR microspectroscopy and chemical imaging. The cystine monoxide band from the products of disulfide oxidation of the amino acid cystine is associated with hair damaging during bleaching process. With increase bleaching time, the band for cystine monoxide shows more intense and larger area in chemical image. The spatially chemical change was investigated in detail by FT-IR microspectroscopy and chemical imaging during the bleached process.

IMPROVEMENT OF BLEACHING OF KAOLIN USING CHELATING AGENTS

Bleaching of the kaolin ore from Shaziling Kaolin Mine in Jiangxi Province of China was studied with the aim of enhancing the quality and value of the ore to meet the requirements from the ceramics manufacturers. Factors affecting the reductive bleaching of kaolin ore with sodium dithionite as the bleaching agent were studied and optimized to increase the whiteness of the kaolin ore from 38. 5% to about 65%. However, it was found that in the conventional bleaching process, a washing step to remove the ferrous ions from the bleached kaolin suspension was indispensable, which made the process complicated and restricted the capacity of the production. In addition, the whiteness of the bleached kaolin products was unstable. To solve the above problems, a new technique with the application of chelating agents in the bleaching process was developed to remove ferrous ions and get rid of the washing step. The bleaching process of kaolin was simplified. The whiteness of the bleached kaolin products was stabilized as well as increased to about 70%. The mechanism of the bleaching process and the action of the chelating agents were discussed.

Effect of Different Bleaching Applications on the Surface Properties and Staining Susceptibility of Dental Composites

The aim of this study was to investigate the effects of two bleaching systems on micro hardness, surface roughness and color stability of two novel dental composites. Ormocer based restorative Admira and nano-filled composite Clearfil Majesty Esthetic were bleached with 10% carbamide peroxide （Opalescence PF） or 35% hydrogen peroxide （Beyond Max 5） and subsequently immersed in four different staining solutions （coffee, tea, red wine, and cola）. Distilled water was used as a control. Color measurements were performed with a spectrophotometer. Vickers micro hardness and roughness data were analyzed with two- way analysis of variance for repeated measures. The analysis of variance was used to compare the color change values. Duncan＇s multiple comparison test was applied to compare the results （a = 5%）. AE~＂ values over 3.3 were considered clinically unacceptable. Micro hardness and surface roughness values of the tested composites were decreased significantly after bleaching applications. Red wine and tea storage caused perceptible discolorations in the composite resin materials after 30 days of 3-hour immersion. Home or office bleaching applications can affect the surface properties of resin composites and accelerate the staining process.

Evaluating the effectiveness of using ClO_2 bleaching as substitution of traditional Cl_2 on PCDD/F reduction in a non-wood pulp and paper mill using reeds as raw materials

The effectiveness of ClO_2 bleaching as a replacement for conventional Cl_2 bleaching,which is intensively practiced in developing countries,to reduce polychlorinated dibenzo-p-dioxins and dibenzofurans(PCDD/Fs)in non-wood pulp and paper mills has not been field tested.The first field study was performed to investigate PCDD/F variations when ClO_2 bleaching was used as a substitute for conventional Cl_2 bleaching in a non-wood pulp and paper mill.It was found that the PCDD/F toxic equivalents(TEQs)in solid and effluent samples were approximately 1.3–14.9 times lower when ClO_2 bleaching was used instead of the conventional Cl_2 bleaching.2,3,7,8-Substituted tetrachlorinated dibenzofurans(2,3,7,8-TCDF)were the dominant contributors to total PCDD/F TEQs in samples from the investigated mill when using conventional Cl_2 bleaching.The formation amounts of 2,3,7,8-TCDF were reduced from 1.56–2.76 pg TEQ/g to 0.02–0.32 pg TEQ/g in solid samples when ClO_2 bleaching was used instead of the conventional Cl_2 bleaching.The replacement of Cl_2 with ClO_2 might decrease the chlorination reactions of dibenzofuran as potential precursors,and thus reduce the formation amounts of 2,3,7,8-TCDF.The results could provide important knowledge for suggesting the best available technique for PCDD/F reduction for non-wood pulp and paper mills in developing countries.

TCF Bleaching of Populus tomentosa Kraft Pulps with H_2O_2 Pretreatment un-der Acid Condition

The process of peroxide bleaching of Populus tomentosa kraft pulp with H2O2 pretreatment under acid condition was studied. The variations of pulp characteristics such as brightness, Kappa number and viscosity during the peroxide bleaching process were discussed and the concept of the A/B value was presented for the first time. The results show that acid pretreatment with H2O2 is essential to improve pulp brightness and avoid viscosity loss. The conclusion is reached that the A/B value has great influence on pulp properties when the total amount of peroxide used in the bleaching process is 2%-5%. Pulp with a high viscosity and brightness can be obtained when A/B is about 0.15.

Treatment of pulpless coloured anterior tooth by bleaching the interior of pulp cavity and filling the cavity with composite

A method of treating pulpless coloured anterior tooth is presented.Most part ofthe coloured dentin of the labial crown was removed and the dental structure was bleachedwith 30% hydrogen peroxide for 5min.The pulp cavity was then filled with whitephoto-curing composite.The result of the treatment is quite satisfactory.With our treatment,the intact contour of the crown and the hardness and gloss of the enamel are preserved.SEM proved that the composite was tightly bound with the enamel of the medial wall of thepulp cavity,forming an entity with the tooth,thus guaranteeing the strength of the crown.

Applications of Enzyme-simulating Copper Complex Catalyst in Low-temperature Scouring/Bleaching of Cotton Knits

An enzyme-stimulating catalyst( PTL) with copper ions( Cu^(2+)) as the activation center and aminophosphonate as ligand was developed and applied in low-temperature scouring/bleaching of cotton knits. The optimal weight ratio of Cu^(2+) to aminophosphonate was 1 ∶75. Via orthodox and single-factor experiments,the most efficient formula for low-temperature scouring/bleaching was composed of 0. 4 g/L high-efficiency degreaser DM-1130,1. 5 g/L PTL,2. 0 g/L sodium hydroxide( NaOH),and 7. 0 g/L 30% hydrogen peroxide( H_2O_2). The PTL could not only increase the whiteness of cotton knits,but also remove pectin to enhance capillary effect.

Optimization of Bleaching Process of Crude Palm Oil by Activated Plantain (<i>Musa paradisiaca</i>) Peel Ash Using Response Surface Methodology

The bleaching of crude palm oil using activated plantain peel ash (APPA) was studied in this work. Historical data design (HDD) in response surface methodology (RSM) experimental design was employed to optimize and correlate the process operating parameters (temperature, time and adsorbent dosage) to the percentage bleaching efficiency. The analysis of the results showed that the quadratic effects of the operating parameters were significant. The optimum condition for the maximum adsorption efficiency of 70.04% was obtained at 160&#176;C temperature, 60 minutes reaction time, and 4 g adsorbent dosage. The predicted bleaching efficiency of 74% was in good agreement with the optimum experimental yield. This study has revealed that APPA is a good source of adsorbent for palm oil bleaching.

Effects of Temperature, pH, Ammonia Nitrogen Content and Salinity on Coral (Acropora millepora ＆ Palythoa sp. ) Bleaching

This study was conducted to investigate the effects of temperature, pH, ammonia nitrogen content and salinity on the bleaching of Acropora millepora and Palythoa sp. This study included two experiments ： Experiment 1 was designed to test the effects of different gradients of temperature, pH, ammonia nitrogen con- tent and salinity at a time point （6h） on Palythoa sp. breeding; and Experiment 2 tested the effects of different levels of temperature, pH, ammonia nitrogen con- tent and salinity at three time points （24, 48 and 72h） on A. millepora bleaching. Before the experiments, A. millepora and Palythoa sp. were washed with filtered seawater （0.45 p,m microporous membrane filtration） and then reared in interior seawater aquurium cylinder. The experiments were carried out when the coral ten- tacles extended and the growth condition were good. The results showed that under high temperature （32 -40 ~C ） , both A. millepora and Palythoa sp. showed drastic reactions in the course of time, reflecting considerably significant stress responses. The number of releasing zooxanthellae increased with increase or de- creaseof the pH value （pH 0, 4, 6, 10, 12） over time. Meanwhile, a relatively thick layer of mucus was found on the upper zone of the seawater and the corals started to bleach. As the concentration of ammonia nitrogen （ NH4 , 0 mmool/L） increased in the course of time, the number of zooxanthellae floating on A. millepo- ra and Palythoa sp. had the tendency to rise. When the salinity level were at 15%o and 40%o for A. miUepora and below 34‰ for Palythoa sp. , a considerable number of zuoxanthellae floated out and had rising trend in their number over time at 24 -72 h and 6 h, respectively. In this occasion, the corals stopped growing and started to bleach. In conclusion, it revealed that temperature, pH, ammonia nitrogen content and salinity are the potential impact factors on coral breeding. It is suggested that, as temperature, pH value and salinity decrease or increase, as well as anmlonia nitrogen content rises, the quantity of phycobiont would be raised, and the bleaching would be more severe.