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PEER-REVIEWED ARTICLE bioresources.com The Effects of H2O2 Bleaching and DTPA Spraying on the Brightness Stability of Hornbeam CMP Pulp Following Accelerated Irradiation Aging Ramin Vaysia and Sayed Aahmad Mirshokraieb Hornbeam chips pulped under CMP conditions at the yield of 85%, then pulps were bleached separately with DTPA and without DTPA, along with hydrogen peroxide. Some of the pulps were bleached with sodium dithionite. Then 60 gr/m2 handsheet were made. A solution of 0.5 % of DTPA was sprayed over a number of handsheets. The handsheets were irradiated for 10, 20, 30, or 40 minutes for optical aging. The results of this study explored that complementary bleaching with sodium dithionite improves optical behavior of the handsheets. Following DTPA solution spraying on the surface of handsheets brightness, opacity and yellowness in improved and K/S ratio and post-color number is decreased. Among different samples and following optical aging, it was found that in long-term aging, DTPA spray has considerable affect can the stability of brightness and increasing it durability against optical deterioration. Key words; DTPA Spray; Brightness Stability; H2O2 Bleaching; Hornbeam; Optical Aging. Contact information: a: Department of Wood and Paper Science, Islamic Azad University, Chalous Branch, Mazandaran, Iran; Corresponding author: vaysi_r452@ yahoo.com. b: Professor, Department of Chemistry, Payame -Noor University, Tehran, , Iran. INTRODUCTION High-yield mechanical and chemi-mechanical pulps are susceptible to photooxidative reactions, which cause the pulps to become discolored and brightness reversion. Newsprint exposed to polychromatic radiation showed the largest amount of yellowing when exposed to irradiation in the wavelength region of 330 to 385 nm (UV-A region); such yellowing has been attributed to the formation of new phenolic and carboxylic groups from quinines radicals during photo-yellowing and long-optical aging (Andrady and Searle 1995). Several factors and structural elements have been proposed or considered as initiators. The main cause of the yellowing in high-yield and mechanical pulps are oxygen, -carbonyl structures, lignin double bond structures, singlet oxygen, various radicals, phenolic groups (catechols), ortho-quinones, para- quinones such as methoxy-p-benzoquinone, lignin -O-4 structures, hydroquinones, and stilbenes formed from the phenylcoumaran-type entities. This phenomenon has been attributed to a lightinduced oxidation of the lignin present in the pulp. Extensive and comprehensive Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,” BioResources##### PEER-REVIEWED ARTICLE bioresources.com research, performed during the last decade, has given not only new information about the photochemical reactions causing yellowing, but also information on potential photostabilizing methods. However, no single approach so far has become technically or economically feasible to meet all the needs of the paper industry (Forsskahl 2000; Carter 1996). The quinone structures and quinone precursors such as hydroquinone and catechols are important reactions in the photo-yellowing process in acetylated groundwood pulps (Monica et al. 1992). Untreated and acetylated aspen CTMP exposed to argon, ambient air, and oxygen atmospheres showed that the degree of photoyellowing of the untreated CTMP decreased when the air in the surrounding atmosphere was replaced with oxygen-free argon, indicating that atmospheric oxygen is not of sole importance for the light-induced discoloration or that trace amount of oxygen is necessary to cause discoloration (Paulsson et al. 2001). In long-term aging, DTPA spray has considerable affect on the stability of brightness, and has the potential to increase its durability against optical deterioration in hornbeam CMP pulp following accelerated irradiation aging (Vaysi et al. 2007). The catalytic activity of Mn+2 and Mn+3 decomposed in hydrogen peroxide by DTPA as the only stabilizer. It was found that the addition of DTPA to a Mn+2 containing system is more effective that if it is added to a Mn+3 containing system. To decrease the catalytic of Mn+3, sodium borohydride and DTPA under an acidic condition were considered to reduce Mn+2 to Mn+3. The effect of pH on using DTPA to decrease Mn induced peroxide decomposition is discussed (Qiu et al. 2003). Fig.1. Photo-yellowing reactions are high- rich lignin pulps. Newsprint exposed to polychromatic radiation showed the largest amount of yellowing when to irradiation in the wavelength region of 330-385 nm (Searle1995). Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,” BioResources##### PEER-REVIEWED ARTICLE bioresources.com EXPERIMENTAL Pulp Hornbeam chips were chosen randomly from a chip pile at Mazandaran Wood and Paper Mill (MWPM) and cooked under CMP conditions (l/w:7, SO2: 116 g/L,NO2: 106 g/L, sodium sulfite :20%, and for 60 minutes in 160 oC), and pulps were prepared at a yield of 85% (Barzan and Soraki 2002; Vaysi et al. 2007). Pulp Bleaching One portion of pulp was bleached using hydrogen peroxide and DTPA as chelating agent according to the method proposed under following conditions: Hydrogen peroxide: 3%, sodium hydroxide on hydrogen peroxide ratio: 0.7% , DTPA charge: 0.3%, Na2SiO3: 3%, pulp consistency: 12%, time: 1 hour, and temperature: 75 oC. Then, pulps were refined to freeness of 300 mL (CSF) by PFI Mill. Some of the pulps were bleached with sodium dithionite. Then 6o gr/m2 hand sheets were made from bleached and unbleached pulp. Then DTPA 0.5% were sprayed on the hand sheets and hand sheet optical properties were measured by standard TAPPI. And 6o gr/m2 hand sheets were made from bleached and unbleached pulp according to TAPPI T 205 om-88 before acetylating (Barzan and Soraki 2002; Vaysi et al. 2007). Irradiation of Paper TAPPI brightness and color change according to the CIELAB color scale (L*,a*,b* values) were measured on 60 g/m2 paper sheets using a Technibrite Micro TB1C spectrophotometer and by using TAPPI Test Method T 224 om-94, respectively. The paper sheets were subjected to accelerated light-induced aging in an apparatus (made by Author) provided with 12 UV-fluorescent lamps ("black light" made by Phillips Co.). The handsheets were irradiated for zero, 10, 20, 30, and 40 minutes for optical aging . The optical characteristics of the handsheets were measured before and after optical aging. Brightness, opacity, yellowness, and greenness were determined according to ISO methods. The specific light scattering (s), light absorption (k) coefficient, k/s ratio, and post-color (PC) number were calculated using the Kubelka-Munk theory. The k/s value and PC number were calculated according to the following equations (Monica et al. 1992; Paulsson et al. 2001; Vaysi et al. 2007), k/s = (1-R )2/ 2 R (1) PC number = 100((k/s)t –(k/s)t=o ) (2) where s is the light scattering coefficient, k is the light absorption coefficient, T is the irradiation time, and R is the reflectivity of an infinite pile of sheets. Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,” BioResources##### bioresources.com PEER-REVIEWED ARTICLE RESULTS AND DISCUSSION The effects of accelerated irradiation treatments on the brightness stability of paper sheets were investigated using bleaching, DTPA spraying and optical aging. The results of this study showed that following accelerated irradiation aging up to 40 hours, absorption coefficient, K/S ratio , opacity , yellowness , a* factor and post color(PC) number were increased, and brightness and greenness were decreased .The post color(PC) number is scale for paper aging, and that is zero for zero hour accelerated aging .In that, the most of post color(PC) number and the least brightness stability were observed in H2O2 bleaching and complementary bleaching with Sodium dithionite In the following bleaching and DTPA spraying on the handsheets, brightness, greenness, opacity improved and K/S ratio and post color(PC) number were decreased. Following aging up to 40 hours, all optical Properties (except brightness) were increased. These changes are more tangible up to 20 hours irradiation (table 1 and figures:2-7). Also complementary bleaching with sodium dithionite improved optical behavior of the hand sheets in short-term aging, but in Following long-aging, the least brightness stability and most of optical deterioration were observed in unbleached paper and H2O2 bleaching H2O2 bleaching and complementary bleaching with Sodium dithionite, too. It is because the oxidizer H2O2 is reduced chromophores (quinones) to acid functional groups in hydrogen peroxide bleaching. The quinone structures and quinine precursors such as hydroquinones and catechols are important reactions in the photo-yellowing process in acetylated ground wood pulps. The quinone structures and quinine precursors such as hydroquinones and catechols are important reactions in the photo-yellowing process in acetylated ground wood pulps. 70 65 Brightness% 60 55 50 45 40 35 30 25 20 0h 10 h 20 h 30 h 40 h Irradiation Unbleached H2O2 bleached+DTPA Spray H2O2 bleached H2O2+Na2S2O4 bleached Fig.3. Changes of brightness in handsheets of Hornbeam CMP pulp following accelerated irradiation aging. Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,” BioResources##### bioresources.com PEER-REVIEWED ARTICLE 140 120 K/S*1000 100 80 60 40 20 0 0h 10 h 20 h 30 h 40 h Irradiation H2O2 bleached H2O2+Na2S2O4 bleached H2O2 bleached+DTPA Spray Fig.3. Changes of K/S in handsheets of Horn beam CMP pulp following accelerated irradiation aging. 110 Opacity% 100 90 80 70 60 50 0h 10 h 20 h 30 h 40 h Irradiation Unbleached H2O2 bleached H2O2 bleached+DTPA Spray H2O2+Na2S2O4 bleached Fig.3. Changes of opacity in handsheets of Horn beam CMP pulp following accelerated irradiation aging. Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,” BioResources##### bioresources.com PEER-REVIEWED ARTICLE 33 Yellowness% 30 27 24 21 18 15 0h 10 h 20 h 30 h 40 h Irradiation Unbleached H2O2 bleached+DTPA Spray H2O2 bleached H2O2+Na2S2O4 bleached Fig.3. Changes of yellowness in handsheets of Hornbeam CMP pulp following accelerated irradiation aging. 2.1 1.6 a* factor 1.1 0.6 0.1 -0.4 -0.9 -1.4 -1.9 0h 10 h 20 h 30 h 40 h Irradiation Unbleached H2O2 bleached+DTPA Spray H2O2 bleached H2O2+Na2S2O4 bleached Fig.3. Changes of a* factor in handsheets of Horn beam CMP pulp following accelerated irradiation aging. Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,” BioResources##### bioresources.com PEER-REVIEWED ARTICLE 7 6 PC*100 5 4 3 2 1 0 0h 10 h 20 h 30 h 40 h Irradiation Unbleached H2O2 bleached+DTPA Spray H2O2 bleached H2O2+Na2S2O4 bleached Fig.3. Changes post color (PC) number in handsheets of Hornbeam CMP pulp following accelerated irradiation aging. Table 1: Changes in Optical Properties of Bleached Hornbeam CMP Pulp Following Accelerated Irradiation Aging. Treatment Brightness% Unbleached Opacity % L* a* b* 94.24 71.59 0.99 12.73 1.87 82.28 82.97 -0.45 13.96 0.5 1.79 85.02 87.92 -0.58 16.45 59.73 2.7 1.69 82.46 86.29 -0.55 15.13 87.63 1.94 2.56 84.13 -5.21 15.61 PC*100 38.73 K/S *1000 232.1 2.4 absorption coef.(m2/kg) 6.95 H2O2 bleached 53.84 69.29 2.2 H2O2+ DTPA Spray H2O2+ Na2S2O4 54.77 56.06 55.72 Optical Aging 51.15 85.21 The catalytic activity of Mn+2 and Mn+3 in hydrogen peroxide decomposed by using DTPA as the only stabilizer. The addition of DTPA to a Mn+2 containing system is more effective that if it is added to a Mn+3 containing system. To decrease the catalytic of Mn+3, sodium borohydride and DTPA under an acidic condition were considered to reduce Mn+2 to Mn+3. The effect of pH on using DTPA to decrease Mn induced peroxide decomposition is discussed [Qiu et al.2005].However, phenolic and carboxylic news groups formation from quinines radicals during photo-yellowing and long-optical aging . This news groups could formation color groups with metallic ions. Those factors are caused less optical properties and brightness reversion. Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,” BioResources##### PEER-REVIEWED ARTICLE bioresources.com Fig.8. Phenolic groups (catechols) from quinones of lignin in hydrogen peroxide and sodium dithionite bleached pulps. The quinone structures and quinine precursors such as hydroquinones and catechols are important reactions in the photo-yellowing process in rich-lignin pulps [EK Monica 1992]. CONCLUSIONS The following conclusions could be drawn from the results of the present study: 1. The results of this study showed that following irradiation up to 40 hours, yellowness, opacity, absorption coefficient, K/S ratio and post color (PC) number increased and brightness decreased 2. Following optical aging up to 40 hours, all optical Properties (except brightness) were increased. The post color (PC) number is scale for paper aging, and that is zero for zero for accelerated aging. These changes are more tangible up to 20 hours irradiation. 3. The DTPA treatment in long-term irradiation and the use sodium dithionite and hydrogen peroxide in short-long aging have better brightness stability. 4. Following long-aging, the least brightness stability and most of optical deterioration were observed in unbleached paper and H2O2 bleaching, too. It is because the oxidizer H2O2 is reduced chromophores (quinones) to acid functional groups in hydrogen peroxide bleaching. 5. Also complementary bleaching with sodium dithionite improved optical behavior of the hand sheets in short-term aging, but in long-aging, the least brightness stability and most of optical deterioration were observed in unbleached paper and H2O2 bleaching and complementary bleaching with Sodium dithionite. Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,” BioResources##### PEER-REVIEWED ARTICLE bioresources.com 6. Following DTPA solution spraying on the surface of hand sheets, brightness, greenness, opacity improved and K/S ratio and post color (PC) number were decreased. In long-term aging, DTPA spray has considerable affect on the stability of brightness and increasing its durability against optical deterioration. DTPA spray has better brightness stability and less brightness reversion and therefore better resistance towards optical deterioration. REFERENCES CITED Andrady,A.L.,and Searle N.D. (1995). "Photoyellowing of Mechanical Pulps; Part 2: Activation Spectra for Light-induced Yellowing of Newsprint Paper by Polychromatic Radiation," TAPPI Journal, 78(5),131-138. Barzan A. and Soraki S.(2002). "Procedure for experimental," Mazandaran Wood and Paper Industries,Sari, Iran, 111-121. Carter Henry A. (1996). 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"Characterization of wood and nonwood mechanical pulps by differential thermal analysis," Journal of Pulp and Paper Science, 29(1 ),17-20. Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,” BioResources##### PEER-REVIEWED ARTICLE bioresources.com Yuan Z. and Mcgarry P.(2002). "Application of yellowing inhibitors to mechanical papers using a pilot liquid application system," Journal of Pulp and Paper Science , 28(5 ),159-166. Yuan Z . , J . Schmidt and Heitner C.(2002). "Compatibility of yellowing inhibitors with several surface- sizing agents, Journal of Pulp and Paper Science, 28 (10), 354-358 . Article submitted: January 2, 2012. Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,” BioResources#####