Peroxide Bleaching Research Articles

Fiber characterization of old corrugated container bleached pulp with laccase and glycine pretreatment

In response to deal with the increasingly serious environmental problems and shortage of fiber raw materials, biological enzyme pretreatment is an effective way to replace a large number of chemical additives to improve the properties of waste paper fibers. Fiber characterization of old corrugated container bleached pulp with laccase and glycine (Lac/Gly) pretreatment was investigated by means of Fourier transform infrared spectroscopy (FTIR), headspace gas chromatography (HSGC), fiber quality measurements (FQA), X-ray diffraction method (XRD), and atomic force microscope (AFM). Results showed that, compared with the control pulp, the whiteness and brightness of the Lac/Gly-treated pulp increased by 16.17% and 7.41%, respectively. And the FTIR showed that Lac/Gly pretreatment promotes the effective removal of lignin by hydrogen peroxide (H2O2) bleaching. The content of carboxyl groups in pulp increased remarkably by 21.92%. The paper physical analysis showed that the paper strength properties have improved remarkably. The fiber quality analyses indicated that the fiber length, coarseness, and curl index changed a little. The XRD analysis showed that the crystallinity decreased by 5.83% due to Lac/Gly treatment. The AFM analysis showed that through Lac/Gly treatment, the lignin and extracts over the fiber surface are decreased significantly.

Effect of Polishing on the Surface Microhardness of Nanohybrid Composite Resins Subjected to 35% Hydrogen Peroxide: An In vitro Study.

ABSTRACTAim:The use of bleaching agents, despite being a conservative treatment, can cause a decrease in the surface microhardness of dental resins, affecting their aesthetics and performance. The aim of this study was to evaluate the in vitro effect of polishing on the surface microhardness of nanohybrid composite resins that were subjected to bleaching with 35% hydrogen peroxide.Materials and Methods:This cross-sectional, in vitro experimental study consisted of 30 composite resin samples made according to ISO 4049-2019 and divided equally into two groups (A and B) which were subjected to 35% hydrogen peroxide bleaching. Group A was subjected to polishing procedure, whereas group B was the control group. The samples were stored in distilled water at 37°C for 24 h. The Vickers microhardness was determined with a load of 100 g-f for 10 s. The data were analyzed with Student’s t-test for independent samples at a confidence level of 95%.Results:The surface microhardness of the group that was subjected to polishing (A) obtained a mean of 78.07 ± 7.96 HV, whereas for the group that was not subjected to polishing (B) the mean was 65.67 ± 5.22 HV. The difference between groups (A and B) was statistically significant (P < 0.001).Conclusion:Nanohybrid composite resins previously subjected to 35% hydrogen peroxide gel significantly increased their surface microhardness when subjected to polishing when compared with unpolished nanohybrid composite resins.

Triple-blinded randomized clinical trial comparing efficacy and tooth sensitivity of in-office and at-home bleaching techniques.

Objective Our study aims to compare the efficacy and tooth sensitivity following in-office (35% hydrogen peroxide) or at-home (10% carbamide peroxide) bleaching treatments both preceded by 2% potassium nitrate (2%KF) desensitizing gel.Methodology 130 volunteers were randomly allocated to a) in-office bleaching and a placebo at-home protocol; or b) in-office placebo and at-home bleaching treatment. 2% KF was applied for 10 min before both treatments.Objective color evaluation was performed (spectrophotometer CIEL*a*b* system and CIEDE2000) to calculate the color change (ΔE00). Subjective evaluation was performed using the VITA classical shade guide followed by shade variation (ΔSGU) at the beginning and end of bleaching treatment and 2 weeks post-bleaching. Tooth sensitivity was daily recorded using a Likert scale varying from 1 (no sensitivity) to 5 (severe sensitivity). Analysis was carried out using non-parametric tests.Results Regarding the color change, at-home bleaching resulted in significant color improvement compared to in-office treatment for the parameters Δb* (p=0.003) and Δa* (p=0.014). Two weeks post-bleaching, the at-home treatment resulted in significant color improvement compared to in-office treatment for the parameters Δb* (p=0.037) and ΔE00 (p=0.033). No differences were observed in either ΔSGU parameters. Concerning sensitivity, patients treated with in-office bleaching reported more tooth sensitivity than the at-home group only on the first day after bleaching started, without significant differences in the other periods evaluated (p>0.05).Conclusions At-home and in-office bleaching, preceded by a desensitizing agent, were effective for vital teeth bleaching and 10% carbamide peroxide produced a higher whitening effect than 35% hydrogen peroxide in the short time evaluation. Tooth sensitivity rates were similar for the two techniques tested.

Kinetics of peroxide bleaching of azorubin in the presence of polyaniline-mangane oxide composite (IV)

Purification of aquatic ecological systems from residues of synthetic dyes used in the textile and printing industry is an urgent problem. Researchers are successfully studying the possibilities of using Fenton and Raff reagents to decolorize aqueous solutions of dyes, they offer various compounds of metals with variable valence, whose ions can serve as catalysts for the decomposition of H 2 O 2 to HO • radicals, which are powerful oxidants. However, the separation of such homogeneous catalysts after interaction with industrial dyes is technically and economically impractical, so there is a need to create insoluble solid catalysts with high adsorption capacity, as exemplified by polymer composites polyaniline - MnO 2 . After the process of purification of water from the dye residues, the solid phase catalyst together with the adsorbed purification products is removed by filtration. We investigated the kinetics of oxidative decolorization of the synthetic dye azorubin in the presence of an adsorbent agent–polyaniline, which was used in the form of its composite with manganese (IV) oxide. The catalytic action of MnO 2 causes the decomposition of hydrogen peroxide to HO• radicals, with their participation the oxidation of dye molecules takes place, products that have almost no color are formed. The polyaniline–MnO 2 composite was synthesized by oxidative polycondensation by adding aniline to a reaction vessel containing a certain amount of MnO 2 powder, which was ground in an aqueous solution of sulfuric acid, the molar ratio of MnO 2 :An = 1:3. Infrared spectroscopy showed that the composition of the polyaniline–MnO 2 composite includes quinoid and benzoid groups of polyaniline and groups of atoms (Mn–O). A number of adsorption absorption peaks between 500 and 800 cm -1 are attributed to the oscillations of Mn–O atoms in MnO 6 octahedra, valence oscillations for quinoid and benzoid forms of PAN are traced at 1 575 and 1 495 cm -1 , peaks at 1 300 and 1 243 cm -1 belong to C–N valence oscillations of the benzoid form (secondary aromatic amine), and the peak at 1 142–1 153 cm -1 is attributed to the quinoid form of doped PAN, the peak at 800 – to the oscillations of atoms in the C–C and C–H bonds of the benzoid form of polyaniline. The kinetics of oxidative decolorization of the dye solution in the presence of equal amounts of the synthesized composite (PAN–MnO 2 ) or mechanical mixtures of the original manganese oxide with pure polyaniline (PAN+MnO 2 ) was studied by UV spectroscopy. It is shown that the rate constants of catalytic decolorization of azorubin with hydrogen peroxide (T = 20 C) when using such catalysts have numerical values of the same order (≈ 10 -5 c -1 ). Increasing the content of PAN in the mechanical mixture from (MnO 2 :PAN = 1:3; k 1 = 6,67 10 -5 s -1 ) to (MnO 2 :PAN = 1:30; k 2 = 8.17 10 -5 s -1 ) leads to some increase in the rate constant of azorubin decolorization reaction, however, in the case of the synthesized composite (MnO 2 :PAN = 1:3; k 3 = 3,17 10 -5 s -1 ) the catalysis efficiency decreases. This fact can be explained by the restriction of access of reagents to the catalytic centers on the surface of manganese oxide particles during the encapsulation of MnO 2 inside the polyaniline matrix during the synthesis of the composite. Keywords : polyaniline, composite, MnO 2 , catalysis, dye azorubin

The Effect of Carbamide Peroxide Bleaching Gel Containing Remineralization Agents on the Bond Strength of Universal Adhesives to Enamel

The Effect of Carbamide Peroxide Bleaching Gel Containing Remineralization Agents on the Bond Strength of Universal Adhesives to Enamel

Effect of deinking and peroxide bleaching on the physical properties of recycled newspapers

Paper recycling for producing a new paper that can be used from old spent paper has gained increased interest, and this process helps prevent the paper from accumulating in landfills, reducing pollution and greenhouse gas emissions. In this work old newspaper (ONP) supplied from Al-Ahram Press is de-inked by washing process using sodium hydroxide, surfactant then hydrogen peroxide was applied to bleach the recycled deinked ONP. Following single-stage bleaching, the fiber properties of the pulp (brightness, tensile, tear strength, and burst index) were determined. The Effect of hydrogen peroxide dose, consistency, and temperature on the pulp brightness were studied. The deinking step produces deinked pulp with low brightness 51.75% ISO and the single-stage peroxide bleaching applied to the deinked ONP pulp could produce pulp with brightness 64.05% ISO at 60 min, 80°C, H2O2 concentration 2% and consistency 20%. The obtained data showed that the brightness of the deinked ONP increases with increasing hydrogen peroxide dose, consistency, and temperature. Also, it was found that the tensile strength and burst index increase by increasing brightness while, tear strength decreased.

Evaluation of the aesthetic effect, enamel microhardness and trans-amelodentinal cytotoxicity of a new bleaching agent for professional use containing trimetaphosphate and fluoride

This study evaluated the effects of calcium gluconate (CaGlu), sodium fluoride (NaF), sodium trimetaphosphate (TMP), and NaF/TMP when added to a 35% hydrogen peroxide (H2O2) bleaching gel on the color change, enamel hardness, penetration and cytotoxicity trans-amelodentinal. Bovine enamel/dentin disks (n = 288) were divided according to the bleaching gel: 35% H2O2; 35% H2O2 + 0.05% NaF; 35% H2O2 + 0.25% TMP; 35% H2O2 + 0.05% NaF + 0.25% TMP; 35% H2O2 + 0.1% NaF + 1% TMP and 35% H2O2 + 2% CaGlu. The bleaching gels were applied thrice (40 min/session) at 7-day intervals between each application. Then, the color change, percentage of surface hardness loss (%SH), cross-sectional hardness (ΔKHN), trans-amelodentinal penetration of H2O2, cell viability and morphology (MDPC-23 odontoblast-like cells), alkaline phosphatase activity (ALP) and deposition of mineralization nodules were determined. The data were submitted to ANOVA, followed by the Student-Newman-Keuls test (p < 0.05). All bleaching gels showed significant color changes after treatment (p < 0.001). Mineral loss (%SH and ΔKHN) and H2O2 penetration were lower for 35% H2O2/0.1% NaF/1% TMP; 35% H2O2/2% CaGlu, meanwhile, showed higher values, compared to the other groups (p < 0.001). Cell viability was around 9%, except for the bleaching gel containing 35% H2O2/0.1% NaF/1% TMP with 12.8% (p < 0.05). ALP was higher for groups containing TMP compared to other whitening gels (p < 0.05). The formation of mineralization nodules was greater for gels containing NaF/TMP or CaGlu (p < 0.05). The alterations of cell morphology were intense for all bleaching gels. It was concluded that the addition of NaF/TMP in-office bleaching did not interfere in bleaching efficacy, reduced enamel demineralization, H2O2 penetration and cytotoxicity.

Calcium Phytate as a Pretreatment for Iron-contaminated Papers Prior to Hydrogen Peroxide Bleaching

ABSTRACT Among bleaching agents available in paper conservation, hydrogen peroxide (HP) is a versatile choice that has many advantages in the removal of discoloration from paper. However, its well-known radical formation in the presence of iron impurities in paper poses the risk of cellulose degradation and color reversion, i.e. return of staining. This study explores a method to diminish undesired HP reactions by adding an additional step using a calcium phytate solution as complexing agent to the recommended treatment sequence. Tests on model papers impregnated with different molar concentrations of iron ions to trace the effects of simulated HP treatments on weight average molar mass, carbonyl group content, and color indicate that the iron phytate complex is sufficiently stable to sustain limited HP bleaching and thereby keeps the iron ions to a certain extent from the reaction system.

Two-Step Bleaching of Jute Yarn and Fabric Using Hydrogen Peroxide and Peracetic Acid

ABSTRACT Bleaching of jute has become essential for making white glossy fabric or base material for coloration intended for value added and diversified products. The conventional hot hydrogen peroxide bleaching process produces white fiber with high loss of tensile strength and impairing the feel. On the other hand newly developed peracetic acid bleaching of jute produces minimum loss of tenacity without impairing the feel but whiteness achieved is slightly low. Partial bleaching of jute was carried out using 25%, 50%, and 75% of the normal dose of bleaching agents and their whiteness index as well as tensile strength were evaluated. In all the cases hydrogen peroxide produced 5–8 grade higher whiteness in HUNTER scale while peracetic acid bleached sample retains higher tensile strength. So, two-step bleaching was carried out using hydrogen peroxide and peracetic acid following single-bath and double-bath processes. Two-step single-bath bleaching of jute fabric using 75% peracetic acid followed by 25% hydrogen peroxide bleaching treatment results in best effect with respect to optical and physical properties.

Formation Mechanism of Bleaching Damage for a Biopolymer: Differences between Sodium Hypochlorite and Hydrogen Peroxide Bleaching Methods for Shellac.

Bleached shellac, a widely used material in food processing and products, was deeply affected in terms of structures and properties by the bleaching method. In the present study, a marked difference was observed between the damage performances of sodium hypochlorite-bleached shellac (SHBS) and hydrogen peroxide-bleached shellac (HPBS). The main bleaching damage reactions of sodium hypochlorite were the addition of double bonds to generate chlorine and the oxidation of hydroxyl to form aldehydes or ketones. In the case of hydrogen peroxide, degradation of shellac resin was caused by the hydrolysis of ester bonds and the oxidation of hydroxyl groups to form aldehydes and ketones, as well as carboxylic acids with deep oxidation. Based on the structural characterization of shellac resin, the bleaching damages were affected by the bleaching agent via the oxidizable groups, such as the unsaturated double bonds, hydroxyl and aldehyde groups in cyclic terpenes, and fatty acid chains. The differences could be attributed to the action of sodium hypochlorite on the hydroxyl group of aldehyde or ketone. Conversely, hydrogen peroxide bleaching oxidized the hydroxyl group and aldehyde group to carboxylic acid and initiated the hydrolysis reaction of the ester bond of the shellac resin, leading to the degradation of the resin. Thus, understanding the mechanism underlying the bleaching damage could provide a scientific basis for the subsequent targeted regulation of bleaching damage.

Enhancement of delignification by ionic liquids pretreatment and modification of hardwood kraft pulp in preparation for bleaching

Ionic liquids (ILs) pretreatment is shown to improve the pulp bleachability and modify the physical strength of the hardwood pulp during the oxygen-chlorine dioxide-hydrogen peroxide (ODP) bleaching. The pretreatment enhanced lignin removal in ODP bleaching, resulting in decreased lignin content of the pretreated pulp. The brightness and strength properties were improved. In particular, the folding strength was increased by 153% relative to the control when the pulp was pretreated by [TEA][HSO4]. The analysis of scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction confirmed the enhancement of delignification in ILs pretreatment by the removal of hemicellulose and lignin on pulp fibers’ surface, and the well-preserved fiber framework of the hardwood pulp fibers during ODP-bleaching.

Novel in-office peroxide-free tooth-whitening gels: bleaching effectiveness, enamel surface alterations, and cell viability

To evaluate the bleaching ability, the effect on enamel surface and cytotoxicity of novel tooth-whitening formulations containing papain, ficin, or bromelain. Forty bovine dental discs (6 cm ×4 cm) were pigmentated and randomly allocated into the following groups (n = 10): Group 1, 20 wt% carbamide peroxide (control); group 2, 1% papain-based whitening; group 3, 1% ficin-based whitening; and group 4, 1% bromelain-based whitening. The whitening gels were prepared and applied on the enamel three times per day once a week, for 4 weeks. Color measurement was obtained by CIEDE2000. Enamel Knoop microhardness and roughness were evaluated. The WST-1 assay was used to evaluate the cell viability of mouse fibroblast cells (L929). Data were statistically analyzed by one-way analysis of variance (ANOVA) and Student Newman Keuls’s post hoc test at α = 0.05 significance level. Bromelain, ficin-based, and carbamide peroxide bleaching gels showed a similar color change (p < 0.001). Higher enamel hardness decrease and higher enamel roughness were caused by the carbamide peroxide (p < 0.05). The experimental whitening gels did not affect cell viability. Tooth bleaching gels containing bromelain, papain, or ficin have substantial clinical potential to be used in the development of peroxide-free tooth whitening gels.

Effect of daily use of fluoridated dentifrice and bleaching gels containing calcium, fluoride, or trimetaphosphate on enamel hardness: an in vitro study.

This study evaluated the effects of calcium gluconate (CaGlu), sodium fluoride (NaF), sodium trimetaphosphate (TMP), and NaF/TMP added to a 35% hydrogen peroxide (HP) bleaching gel for the reduction in enamel demineralization in vitro, with and without the use of a fluoridated dentifrice. Enamel blocks (n = 100) were obtained from bovine incisors (n = 200) after flattening and subjected to initial surface hardness (SH) analysis. The blocks were divided according to the bleaching gel (35% HP; 35% HP + 0.05% NaF; 35% HP + 0.25% TMP; 35% HP + 0.05% NaF + 0.25% TMP; 35% HP + 2% CaGlu) and were treated with ether non-fluoridated or fluoridated (1100ppm) dentifrice. The bleaching gels were applied thrice (40min/session) at the intervals of 7days between each application. After 21days, the final SH for the calculation of the percentage of SH loss (%SH) and cross-sectional hardness for the evaluation of the integrated hardness area (IH) were determined. Bleaching containing HP + NaF + TMP presented lowest %SH (p < 0.001), regardless of the dentifrice used. HP + NaF + TMP bleaching gel led to lower subsurface enamel mineral loss (IH) compared to the other groups (p < 0.001), and these did not differ from each other (p > 0.05). Daily use of fluoride dentifrice led to higher IH values (p < 0.001), regardless of the bleaching gels. The addition of NaF/TMP to a 35% HP bleaching gel remarkably reduced the mineral loss compared to the cases of the other bleaching gels, regardless of dentifrice. The association of TMP/NaF can be used as a strategy for reducing mineral loss during the bleaching procedure, even without the daily use of fluoride dentifrice.

Pulping of bagasse (Saccrarum officinarum), kash (Saccharum spontaneum) and corn stalks (Zea mays)

Bangladesh being a small and populated country faces shortage of fibrous raw materials. The only bagasse-based pulp mill was forced to close down due to inadequate supply of bagasse. In this context, similar alternative raw materials need to be evaluated to support small scale pulp mills in this country. Whole bagasse, kash and corn stalks were assessed in terms of their chemical and morphological characteristics. These fibres showed a moderate level of α-cellulose (43.3, 39.3 and 35.1% respectively) and low level of lignin content (~20%). Alkaline oxidation showed that the lignin of these non-woods was composed of high proportion of p-hydroxyphenyl propane unit. The fiber length of whole bagasse, kash and corn stalks was 1.36 ​mm, 0.86 and 0.90 ​mm, respectively. Soda-anthraquinone (AQ) and formic acid/peroxyformic acid (FA/PFA) pulping processes of these three non-woods were evaluated. FA/PFA process showed higher pulp yield than soda-AQ process. Corn stalk was easier to delignify in soda-AQ process, and showed the lowest pulp yield and kappa number. The papermaking properties of these pulps showed good tensile index (75–85 ​N ​m/g) and moderate tear index (4.5–6 ​mN/m2/g). Brightness of these pulps reached to 84–90% in D(EP)D bleaching and 73–85% in alkaline peroxide bleaching.

Effectiveness and SEM-EDX analysis following bleaching with an experimental bleaching gel containing titanium dioxide and/or chitosan.

The aim of this study was to evaluate the bleaching effectiveness and mineral alterations following the use of experimental bleaching gels that included 6% hydrogen peroxide (HP), titanium dioxide (TiO2) and/or chitosan in comparison with the routinely used 35% HP bleaching gel. Thirty-six maxillary anterior teeth were divided into three groups according to bleaching agent as follows: Group 1: 6% HP + TiO2, Group 2: 6% HP + TiO2 + chitosan, Group 3: 35% HP. Tooth colour was measured with a spectrophotometer before bleaching and after sessions one and two on days 14 and 30, respectively. Colour changes were assessed with the CIEDE2000 and CIELab formulas. Mineral analysis was performed with a scanning electron microscopy-energy dispersive X-ray (SEM-EDX) device before and 14days after application. The enamel surfaces of randomly selected samples from each group were analysed by SEM. Two-way ANOVA was used to compare differences between groups. All tested materials resulted in significantly increased bleaching compared to the initial colour values (p < 0.05). Group 3 showed significantly more whitening compared to the other groups after the first and second sessions (p < 0.05). However, Group 2 presented prolonged whitening efficiency and reached a bleaching level similar to the 35% HP treatment after 14 and 30days. The results of the CIEDE2000 and CIELab formulas were found to be correlated (r > 0.6). The increases in Ca were similar in Groups 2 and 3 (p > 0.05) and were significantly higher than that in Group 1 (p < 0.05). p was similarly decreased among all groups (p > 0.05). The combination of 6% HP, chitosan and TiO2 appears to constitute a promising material for tooth whitening, showing good bleaching efficiency and acceptable mineral alterations.

Evaluation and Optimization of Kraft Delignification and Single Stage Hydrogen Peroxide Bleaching for Ethiopian Sugarcane Bagasse

ABSTRACT The current study investigated the Ethiopian sugarcane bagasse during its delignification using the Kraft pulping process and bleaching by single stage hydrogen peroxide process. The multilevel categoric experimental design was used to appraise the effects of the independent process variables (temperature, NaOH concentration, and time) on the pulp yield and kappa number during the Kraft pulping process. The central composite experimental design of response surface methodology was used to appraise the effects of independent bleaching variables (bleaching temperature, H2O2 concentration, and time) on the pulp yield, brightness, and whiteness during the bleaching process. The optimal pulp yield was 38.41% with 17.68 kappa number. The bleached pulp yield for the pulp with kappa number of 17.68 and the pulp with kappa number of 8.41 were 84.12% and 83.91%, respectively. The brightness and whiteness for the pulp with kappa number of 17.68 were 61.92% and 85.36%, respectively. Similarly, for the pulp with a kappa number of 8.41, the brightness and whiteness were 68.35% and 91.43%, respectively. Paper from the pulp with kappa number of 17.68 has higher tensile, burst, and tear strength. The study shows the promising utilization of the Ethiopian sugarcane bagasse for paper production via the Kraft delignification and single stage hydrogen peroxide bleaching.

A Comparative Study on the Cost Effectiveness and Whiteness Effect of Homemade Bleach Mixture Vs. Industrial Bleach

Chlorine is used in the manufacture of a wide range of consumer products, about two-thirds of them organic chemicals such as polyvinyl chloride, and many intermediates for production of plastics and other end products which do not contain the element. As a common disinfectant, elemental chlorine and chlorine-generating compounds are used more directly in swimming pools to keep them clean and sanitary. it was reported by the World Health Organization that Bleach is one of the leading substances for accidental poisoning amongst children. Thus, in this work, the authors conducted comparative study whether this homemade alternative for bleach will turn out to be as effective as it’s Industrial Chlorine-Based. The researchers are also looking to compare both mixtures in terms of Costs, as well as Health & Safety risk. In this study, the researchers focused only on the quantitative method of research involving numerical data analyzed using statistical tests. Key results showed that the researchers determined that the homemade mixture of Hydrogen peroxide bleach was more cost effective while being almost as effective as the Industrial bleach.

BLEACHING OF FABRICS PRODUCED FROM CASEIN FIBERS

The pH of milk fibers, which can be obtained even from the protein of sour milk, is compatible with the human body. Besides being ecological, they have biodegradable properties. In this paper the influence of different bleaching conditions with hydrogen peroxide and thioureadioxide (TUDO) on the whiteness of casein fiber fabric was investigated. Bleaching was carried out both conventionally and with microwave energy. Whiteness, bursting strength, hydrophilicity, and chemical oxygen demand (COD) values were determined and compared. The structures of the untreated and treated casein fabrics were investigated with Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The effect of bleaching on the structure of casein fabric was investigated with scanning electron microscopy (SEM). The loss of strength in milk fiber based fabrics which have been bleached with peroxide in acidic medium is less than the loss in bleaching in basic medium. Microwave energy can produce whiteness levels obtained by conventional method in much shorter periods. Strength losses are also less. The air permeability test results show that the air permeability of casein fiber based fabric samples decreases with increasing processing temperature and processing time. Careful selection of process temperature and duration is important for milk fibers as well as for wool fibers. When working with milk fibers it is recommended to test the dimension peroxide bleaching change according to the process conditions.

Technical and environmental improvement of the bleaching sequence of dissolving pulp for fibre production

Reactivity of dissolving pulp is one of the main parameters to determine its availability to be transformed into viscose. It is related to the use of carbon disulphide (CS2). An industrial sequential totally chlorine free bleaching process is used as case study. It is carried out in two stages: (1) Alkaline extraction (EOP) and (2) peroxide bleaching (PO). In order to assess how to decrease the use of carbon disulphide, several experiments were performed at laboratory scale for the two stages mentioned before by modifying the operating conditions: NaOH and H2O2 dosages, time and temperature. Reactivity using a modified Fock’s method and pentosan content was analysed along with quality pulp parameters: α-cellulose, viscosity and lignin content (kappa number). Results showed that reactivity increases through the bleaching process and varies with the chemical dosage in both stages. Pulp obtained at the best conditions had the following characteristics: reactivity, 95.3%; α-cellulose 91.17%; intrinsic viscosity, 448 mL/g; kappa number, 1.81 and pentosan content 2.86%, and as a result, CS2 usage was reduced by 11.88%. At the best conditions obtained in this work, NaOH dosage in PO stage was reduced to zero and temperature was slightly lower, when compared with industrial operating conditions.

Effects of 16% Carbamide Peroxide Bleaching on the Surface Properties of Glazed Glassy Matrix Ceramics.

Objective To determine the influence of the home bleaching agent, Opalescence PF, on the surface roughness and microhardness of glazed glassy matrix CAD-CAM ceramics. Materials and Methods. The 28 sintered leucite- and lithium disilicate-reinforced ceramic specimens (IPS Empress CAD and IPS e.max CAD) were divided into control and bleached groups. The home bleaching agent was applied to specimens of bleached groups for 7 days. The surface roughness and microhardness of all specimens were measured. A scanning electron microscope was used to evaluate the surface properties. The data were statistically analyzed by two-way ANOVA. Results The control e.max CAD showed the lowest surface roughness values. For both Empress and e.max CAD, surface roughness was significantly higher for the bleached group (p < 0.05). No significant differences in microhardness were observed. Conclusions According to our study, patients should be careful when using home bleaching agents because whitening agents can affect the mechanical properties of full ceramic restorations like e.max CAD and Empress CAD. Ceramic polishing may be required in clinical situations where ceramic restorations are accidentally exposed to bleaching gels.