Electron beam irradiation (EBI) is an alternative treatment for intrinsic viscosity (IV) control in cellulose pulps, but has never been integrated in full bleaching sequences for comparison to conventional methods.
Carbohydrate Polymers 265 (2021) 118037 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Partial exchange of ozone by electron beam irradiation shows better viscosity control and less oxidation in cellulose upgrade scenarios Oliver P Sarosi a, 1, Daniela Bammer a, 1, Elisabeth Fitz a, 1, Antje Potthast b, * a Kompetenzzentrum Holz GmbH, Altenbergerstraße 69, A-4040, Linz, Austria Institute of Chemistry of Renewable Resources, Department of Chemistry, University of Natural Resources and Life Sciences, Konrad-Lorenz-Straße 24, A-3430, Tulln, Austria b A R T I C L E I N F O A B S T R A C T Keywords: Kraft pulp Xylan Hexenuronic acid Chemical-free Bleaching Electron beam irradiation (EBI) is an alternative treatment for intrinsic viscosity (IV) control in cellulose pulps, but has never been integrated in full bleaching sequences for comparison to conventional methods Both euca lyptus kraft (EK) paper pulp and beech sulfite (BS) dissolving pulp were subjected to totally chlorine free (TCF) bleaching sequences comprising either EBI, ozone, or both for IV control Additionally, effects of EBI on hex enuronic acid (HexA) and xylan were investigated IV was adjusted to 450–500 mL g− and properties including carbonyl content, kappa, brightness, alkali-resistance and sugar composition were compared Pulps produced with EBI had a higher alkali-resistance, uniformity and less cellulose oxidation However, the degree of bleaching (DoB) was low without the use of ozone HexA content in a birch pulp was halved by EBI Isolated xylans were more resistant to irradiation than cellulose with little decrease of molar masses and moderate oxidation Introduction With an increasing demand for environmentally friendly textiles, the market for regenerated cellulose fibers (RCF) is projected to show a 4.2 % compounded annual growth rate, despite the recent events sur rounding COVID-19 (GlobeNewswire, 2020) To enter the RCF market, the upgrade of existing low-value paper pulp mills to high-value dis solving pulp mills or swing mill operation has been considered in the past (Lundberg, Axelsson, Mahmoudkhani, & Berntsson, 2012; Sappi Limited, 2013) Converting paper pulp to dissolving pulp requires the removal of hemicellulose through either acid prehydrolysis before pulping or alkaline extraction or enzymatic degradation during bleaching (Hut terer, Schild, & Potthast, 2016; Hutterer, Kliba, Punz, Fackler, & Pot thast, 2017; Sixta, 2006) Dissolving pulp generally requires a high content of α-cellulose, a brightness above 90%ISO, a narrow molecular weight distribution (MWD), and low IV Thus, an upgraded paper mill or swing mill needs a method for IV reduction, which can be achieved by adjusting the process parameters, such as cooking intensity, ozone charge during TCF bleaching or dwell times during steeping and accel erated aging However, intensified cooking conditions lead to a sub stantial cellulose yield loss and a conversion of α-cellulose to undesirable alkali-soluble fragments (Agarwal & Gustafson, 1997; Kubes, Fleming, Macleod, Bolker, & Werthemann, 1983) Furthermore, alkaline steeping and pulp pre-aging oxidize the pulp, introducing both carbonyl and carboxyl groups, which are responsible for pulp brightness reversion ăf, So ăderlund, & Germgồrd, 2006; Mozdynieư (Ahn et al., 2019; Kvarnlo wicz, Nieminen, & Sixta, 2013) Ozone rapidly decomposes under aqueous conditions during bleaching, yielding various radical and peroxo-species (Staehelin, Buehler, & Hoigne, 1984) Ozone itself and all subsequent radical spe cies can cleave the glycosidic bond of cellulose, especially if the tem perature is raised and transition metals such as iron and cobalt are present, favoring the Fenton-type decomposition of ozone (Kishimoto & Abbreviations: BS, beech sulfite pulp; CCOA, [2-(2-aminooxyethoxy)-ethoxy]-amide; DoB, degree of bleaching; DP, degree of polymerization; DS, degree of substitution; EBI, electron beam irradiation; ECF, elemental chlorine free; EK, eucalyptus kraft pulp; FDAM, 9H-fluoren-2-yl-diazomethane; IV, intrinsic viscosity; HexA, hexenuronic acid; KX, kraft xylan; Mn, number average molecular weight; Mw, weight average molecular weight; MWD, molecular weight distribution; odtp, oven-dried ton of pulp; SX, sulfite xylan; REG, reducing end group; RCF, regenerated cellulose fiber; TCF, totally chlorine-free * Corresponding author at: Muthgasse 18, Department Chemie, A-1190, Vienna, Austria E-mail addresses: o.sarosi@wood-kplus.at (O.P Sarosi), d.bammer@wood-kplus.at (D Bammer), e.fitz@wood-kplus.at (E Fitz), antje.potthast@boku.ac.at (A Potthast) Werkstraße 2, A-4860, Lenzing https://doi.org/10.1016/j.carbpol.2021.118037 Received February 2021; Received in revised form 15 March 2021; Accepted April 2021 Available online April 2021 0144-8617/© 2021 The Authors Published by Elsevier Ltd This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) O.P Sarosi et al Carbohydrate Polymers 265 (2021) 118037 Nakatsubo, 1998; Ni, Kang, & van Heiningen, 1996; Tripathi, Bhardwaj, & Ghatak, 2018) Initially, the ozone treatment shows a higher reaction rate towards residual lignin and after its depletion, cellulose degradation is promoted, offering dose-dependent IV control (Kang, Zhang, Ni, & van Heiningen, 1995; Lachenal, Mishra, & Chirat, 2013) However, an increased rate of cellulose degradation is accompanied by a similar rate of undesirable carbonyl group formation due to the low selectivity of ozone and its decomposition products (Pouyet, Chirat, Potthast, & Lachenal, 2014; Zhang, Ni, & van Heiningen, 2000) Since ozone has such a rapid reaction rate, its diffusion into the pulp and thus cellulose degradation is limited to amorphous and crystalline surface regions, leading to broadening of the MWD and, in extreme cases, to a bimodal distribution of cellulose due to the unequal treatment of different cel ¨holm, & Lindstro ¨m, 2001) lulose fractions (Berggren, Berthold, Sjo In contrast, γ-irradiation and EBI homogeneously penetrate the pulp on a macroscopic and microscopic level, leading to ionization in both amorphous and crystalline regions (Hammer, Christensen, Conroy, King, & Pogue, 2011; Yang, Zhang, Wei, Shao, & Hu, 2010) EBI causes radical formation throughout the cellulose molecule, which leads to cleavage of the glycosidic bond at statistically distributed positions along the cel lulose chain (Burkart, 1999) Not only can the IV be adjusted to a desirable level through a dose-effect relationship, but also the dispersity (Ð) is reduced (Sarosi, Bischof, & Potthast, 2020; Sixta, Andrea, & Kraft, 2007) Additionally, EBI treatments of cellulosic pulps have a high yield while avoiding degradation to the monomer level and a statistical preference for longer cellulose chains, retaining high contents of α-cel lulose at irradiation intensities of 20 kGy or below (Sarosi et al., 2020; Yang et al., 2010) EBI has been reported to have oxidative effects, leading to the formation of carbonyl groups on the cellulose backbone at elevated irradiation levels of 50 kGy and above (Henniges, Hasani, Potthast, Westman, & Rosenau, 2013) However, by differentiation be tween newly formed reducing end groups (REGs) and keto groups from ăhrling, Potthast, Rosenau, Lange, oxidation by the CCOA method (Ro Ebner et al., 2002), it has been shown that at low irradiation levels of 20 kGy or below, the oxidation by EBI is lower than the detection limit, refuting its long believed highly-oxidative nature (Henniges et al., 2013) In a previous study, the protective effect of residual pulp com ponents, such as hemicellulose and lignin, towards chain scission and oxidation were investigated (Sarosi et al., 2020) Hemicellulose was found to protect cellulose from chain scission and backbone oxidation, which was attributed to its sacrificial function as a protective barrier, shielding cellulose from radicals from the surrounding water While for lignosulfonates the antioxidant properties of residual lignin had a beneficial effect, lignin in kraft pulps caused backbone oxidation Another important species to observe is HexA It is formed from 4-O-methylglucuronic acid during alkaline kraft pulping and causes additional consumption of bleaching chemicals and brightness insta bility when not removed (Jiang, Lierop, & Robson, 2000; Rosenau et al., 2017) HexAs are hydrolyzed during hot acid and ozone stages, and while their role in pulping and bleaching has been sufficiently studied (Antes & Joutsimo, 2015; Brogdon, 2009; Gomes, Longue, Colodette, & Ribeiro, 2014), the impact of ionizing irradiation on HexAs has only rarely been investigated (Tsuji-Katsukawa, Miyawaki, & Koyanagi, 2012) The goal of this study was to highlight benefits and drawbacks of IV control by EBI when using it as an integral part of TCF bleaching se quences as a full or partial replacement of ozone Experimental focus was put on the controlled reduction of IV to provide a chemical-free and more homogeneous and more flexible alternative to ozone for cellulose depolymerization in paper pulp upgrade applications The final pulp properties of a eucalyptus (Eucalyptus globulus) kraft paper and a beech (Fagus sylvatica) sulfite dissolving pulp were compared after using EBI and/or ozone for IV adjustment Further experiments were performed to elucidate the impact of EBI on isolated xylan and HexAs Using EBI as a partial or full replacement of ozone may facilitate IV control especially in high-Mw kraft pulps, which allows for process debottlenecking and chemical savings during bleaching Experimental 2.1 Pulps Two different pulps were used for this study Both oxygen-bleached eucalyptus (Eucalyptus globulus) kraft paper pulp (EK) and oxygenbleached beech (Fagus sylvatica) sulfite dissolving pulp (BS) were generously contributed from an industry partner as research samples Both pulps were never-dried and lab-washed In between use, all pulps were stored at − 20 ◦ C After each bleaching stage, the IV was measured to assure correct progression HexA-rich birch kraft pulp was generously contributed by the University of Natural Resources and Life Sciences (Vienna, Austria) 2.2 Xylan Beech sulfite xylan was isolated from steeping lye by acidic precip itation Eucalyptus kraft xylan was prepared by cold caustic extraction and acidic precipitation of a fully bleached paper pulp 300 g of air-dried pulp were subjected to CCE by swirling at 2.5 % consistency for 30 at 25 ◦ C, using 10 % (w/v) NaOH lye The dissolved xylan was separated by filtration and regenerated by acidification to pH 2.5 using 20 % H2SO4 The sediment xylan was purified by repeated cycles of centrifugation and stirring in fresh softened water Finally, the xylan was dried at 60 ◦ C over-night, which resulted in a yield of 22 g xylan 2.3 Bleaching stages 2.3.1 Irradiation EBI was conducted at room temperature as described in a previous study (Sarosi et al., 2020) Irradiation was performed at Mediscan GmbH (Kremsmünster, Austria) using a Rhodotron TT100-IBA-X electron accelerator according to EN ISO 13485 and ISO 11137 Pulps were prepared for irradiation by forming pulp sheets with a thickness of 2− cm, a diameter of 20 cm and a moisture content of 72–75 % The pulp sheets were attached to cardboard panels and positioned in vertical irradiation trays To guarantee homogeneous irradiation, total pulp thickness was kept below cm The irradiation dose was set to (and verified by a dosimeter as) either 1.25 kGy (1.30 kGy) or 2.5 kGy (2.52 kGy) for the beech sulfite pulp and 5.0 kGy (5.2 kGy) or 10.0 kGy (10.3 kGy) for the EK pulp Irradiated pulps were swirled in hot water at % consistency for and then filtered For irradiation of HexA-rich birch kraft pulp and xylan, ~1.5 g of dry sample was filled into micro reaction tubes (PP) and attached to cardboard sheets before passing through the electron beam Additional irradiation levels were set to (and verified as) 50.0 kGy (50.2 kGy), 100 kGy (101.3 kGy) or 200 kGy (202.0 kGy) Doses above 50 kGy were applied by multiple passes at reduced doses on alternating sides 2.3.2 A-stage EK pulps received a sulfuric acid stage for metal removal before ozone or peroxide treatment For hot acid treatments, preheated pulp and softened water were mixed in plastic bottles (PP) at 3.0 % consis tency and the pH was slowly adjusted to 2.5 using sulfuric acid (100 g L− 1) The bottles were sealed, mixed thoroughly by vigorous shaking and incubated for 30 at 60 ◦ C (A) or 90 ◦ C (A-hot), depending on whether or not an IV reduction, respectively, was desired, with repeated shaking after 15 The reaction was terminated by vacuum filtration of the bottle contents over a quartz frit and washing of the pulp 4–6 times with double the pulp volume of hot, softened water and vacuum suction between washes 2.3.3 Z-Stage Ozone bleaching was conducted in a medium-consistency (MC) O.P Sarosi et al Carbohydrate Polymers 265 (2021) 118037 mixer with closed lid and thorough pulp fluidization The treatment and subsequent pulp workup were performed by trained lab workers The treatment conditions were the following: 4.0–16.9 kg odtp− (kilogram per oven-dried ton of pulp) of ozone charge, depending on the type of pulp and treatment route, pH 2.5, 45 ◦ C, 10 % consistency The total ozone charge for each pulp was split into smaller partial charges and IV was measured in-between charges while the pulp remained in the reactor Once the IV was adjusted to a satisfactory level, the pulp was filtered and washed 4–6 times with double the pulp volume of hot, softened water Actual ozone consumption was determined by streaming the gaseous phase before and after bleaching through a potassium iodide solution and titrating against sodium thiosulfate using starch as indicator GPC data according to: REG = × 106 Mn (1) where Mn is the number average molecular weight HexA analysis relied on the available TAPPI standard using spec troscopic quantification after hydrolysis (Chai, Zhu, & Li, 2001; TAPPI, 2007) Results & discussion 3.1 Bleaching sequence conduct and observations The goal of the adjustment was to achieve IV between 450–500 mL g− (degree of polymerization (DP) 1045–1205), which is suitable for RCF processes To investigate the differences between EBI and ozone during a full bleaching sequence, three approaches were chosen for each pulp Table summarizes the different sequences for each pulp Oxygendelignified pulps were used as the starting point for all experiments The first variant used EBI as a full replacement of ozone Electron doses were calculated based on dose-effect fit functions from previous experiments with similar pulps (Sarosi et al., 2020) The second approach used both EBI and ozone in lower doses to represent the integration of EBI in an existing bleaching sequence and to highlight potential chemical savings and quality improvements Finally, the third sequence applied a con ventional sequence based on ozone as reference Xylan removal from the paper pulps can be performed by cold caustic extraction and enzymatic treatments after TCF bleaching, but was omitted in this study to avoid the interference of effects such as additional IV reduction, changes in Ð, or alteration of the chemical composition (Duan, Verma, Li, Ma, & Ni, 2016; Hutterer et al., 2016) Fig shows the IV decrease caused by each stage EBI of the kraft pulp delivered values within the calculated target range A dose of 10 kGy halved the IV, while the kGy treatment achieved 87 % of that IV reduction This is in accordance with previous studies, since EBI is known to randomly cleave the cellulose chain, which is expressed by a linear increase of the number of chain scissions and an exponential decrease of IV and weight average molecular weight (Mw) (Chen, Ma, Li, Miao, & Huang, 2017; Henniges, Okubayashi, Rosenau, & Potthast, 2012) Since BS had a lower initial IV, a smaller irradiation dose was applied However, the sulfite pulp showed a similar IV decrease by both 1.25 and 2.5 kGy, despite precise dose control This may be ascribed to the high sensitivity of Mw at the initial, low dose range In some cases, the IV was slightly increased after hot acid (A) or the first ozone (Z) stage One explanation may lie in the hydrolysis and removal of short chains, thus increasing the median chain length However, the sugar outflow (Fig 2, Table 3) did not indicate significant carbohydrate release in those stages and it remains unclear where this IV increase originates from The ozone stages were conducted by applying stepwise charges with IV measurements in between, which allowed for precise control When comparing the IV reduction capacity of ozone treatments expressed as the quotient of %IV reduction and ozone dose (data not shown), the presented results fall in line with numbers that other researchers have found during the ozone treatment of comparable pulps (He, Liua, & Tian, 2018; Pouyet et al., 2014; Tripathi et al., 2018) By incremental application of ozone charges it is shown that dose-normalized %IV reduction of BS pulps is larger after the first charge, while EK pulps receive an equal reduction intensity with each charge This may indicate that BS pulp has approximated a kinetic bottleneck after the first ozone stage In contrast, the high residual lignin and xylan content in EK partially protect cellulose from degradation, which inhibits %IV decrease, resulting in a lower rate across all ozone stages Additionally, data from the literature suggests that fiber acces sibility and pulp reactivity of a paper pulp is typically much lower than that of a dissolving pulp, limiting ozone diffusion in the former (He 2.3.4 P-stage Every sequence was terminated by a strong hydrogen peroxide stage with constant charges to both increase the DoB and stabilize the IV by β-elimination of carbonyl “hot-spots” on the cellulose backbone (Yang, 2016) Hydrogen peroxide bleaching was conducted in plastic bottles (PP) The treatment conditions were the following: kg odtp− hydrogen peroxide, kg odtp− sodium hydroxide, 10 % consistency, 90 ◦ C, 180 with thorough shaking every 30 Both pulp and soft ened water were pre-heated and the calibrated amounts of hydrogen peroxide (~35 %, exact content was measured before use) and sodium hydroxide stock solution (50 g L− 1) were added to the water just before mixing The bottle was sealed, shaken vigorously and incubated at 90 ◦ C for 180 with additionally shaking every 30 The reaction was terminated by vacuum filtration of the bottle contents over a quartz frit and washing of the pulp between 4–6 times with double the pulp volume of hot, softened water Contact with atmospheric oxygen at high alka linity was minimized by working quickly and keeping the pulp covered during workup Residual hydrogen peroxide and alkalinity were deter mined by titration as described above or against 0.1 M HCl, respectively In cases where the peroxide was not completely consumed due to low pH, the bleaching stage was repeated, employing the calculated residual hydrogen peroxide charge After hydrogen peroxide treatment, the bleaching sequence was terminated by swirling the pulp at % consis tency for 10 in hot water and adjusting the pH to below 3.0 using SO2-infused water with subsequent washing 2.4 Pulp analysis Kappa number is measured according to TAPPI T236cm-85 where pulp chromophores are reacted with a fixed amount of KMnO4 solution and its consumption is evaluated by neutralization with KI followed by titration against Na2S2O3 Pulp, brightness, is analyzed according to ISO 2470-1:2009 where the reflectiveness of uniform pulp sheets is measured optically and IV was were measured according to TAPPI T236cm-85, ISO 2470-1:2009 and ISO 5351 5351, respectively, which uses rheological data from pulp solutions in cupri-ethylenediamine and a flow-through viscometer Alkali-resistant fractions R10 and R18 were determined according to DIN 54355, which analyzes the pulp solubility in 10 % or 18 % NaOH solution, respectively Cellulose crystallinity was measured by FT-Raman spectroscopy with reference data from X-ray ăder et al., 2006) wide angle scattering (Ro The sugar composition of pulps and aqueous samples was analyzed by total hydrolysis and HPLC as previously described (Sarosi et al., 2020) Measuring the MWD was coupled to fluorescence labeling of carbonyl or carboxyl groups, as described in the CCOA or FDAM method, ăhrling, Potthast, Rosenau, Lange, respectively (Bohrn et al., 2006; Ro Borgards et al., 2002) Instrumentation, settings and data evaluation was performed as previously described (Sarosi et al., 2020) For fluorescence detection of FDAM-labelled samples, a different fluorescence detector, RF 535 (Shimadzu, Japan), was used at λex 280 nm and λem 312 nm As a rough estimation, the number of REGs can be calculated from O.P Sarosi et al Carbohydrate Polymers 265 (2021) 118037 Table General properties of the investigated hardwood pulps before treatment Pulp Mw (GPC-MALS) (kg mol− 1) IV (mL g− 1) Kappa number Brightness (%) R10; R18 (%) Hemicellulose content (%) Oxygen-bleached eucalyptus kraft pulp (EK) Oxygen-bleached beech sulfite pulp (BS) 466 336 943 643 8.6 1.9 63.5 77.5 89.3; 91.6 89.1; 93.8 19.0 3.4 and highest in EK pulps, with values of 0.8 % for EK-EBI and EKI-mixed and 1.8 % for EK-ozone Table Pulp treatment sequences and electron and ozone dose *The first number is the measured actual dose that was required and the second number in parentheses is the initially calculated dose requirement Pulp Bleaching sequence Electron dose (kGy)* Ozone charge (kg odtp− 1) Name EK EK EK BS BS BS OO-EBI-A-P OO-EBI-A-Z-P OO-A(hot)-Z-P EO-EBI-P EO-EBI-Z-P EO-Z-P 10.3 (10.0) 5.2 (5.0) – 2.52 (2.5) 1.3 (1.25) – – 6.4 16.9 – 4.4 4.0 EK-EBI EK-mixed EK-ozone BS-EBI BS-mixed BS-ozone 3.2 Comparison of final pulp properties 3.2.1 IV, MWD and carbonyl group distribution After completing each bleaching sequence, the pulps were analyzed by the CCOA method (Table 4, Fig 3) The underlying GPC data shows, that all pulps have an Mw of 227–295 kg mol− 1, which translates to calculated IVs of 561–685 mL g− This deviates significantly from the measurements by the cupri-ethylenediamine (CUEN) method, which showed similar ratios between the pulps, albeit 150–200 mL g− lower numbers due to β-elimination in the CUEN solution In both EK and BS pulps, dispersity is significantly higher when ozone was used for IV control This effect is aggravated in the EK pulps, where a stronger IV reduction was required This is a result of the diffusion behavior and high reactivity of ozone, which limits polysaccharide degradation to short-chain amorphous and outer crystalline regions, leaving long-chain core regions mostly intact Thus, EK-ozone shows the strongest peak broadening as it required the highest dose of ozone Additionally, it is the only pulp that showed slight degradation to the monomer level during the Z-stage, caused by the prolonged dwell times in the acidic reactor as a consequence of the step-wise process conduct (Fig 2) EBI treatments led to a statistically distributed increase of carbonyl groups, raising the carbonyl profiles by both backbone oxidation and new REG This is most visible in, but not limited to, the low-Mw region While carboxy group formation by EBI has been reported for amorphous cotton materials, lignocellulosic pulps barely undergo carboxyl group formation at low irradiation doses, especially in hardwood pulps in which a high hemicellulose content is present (Bouchard, M´ ethot, & Jordan, 2006) This is caused by the limited diffusion of molecular ox ygen inside the material Hence, EBI in the present study delivers carbonyl groups as the major oxidation product at the given irradiation levels In analogy to the IV reduction, oxidation is heterogeneous for chemical treatments (Potthast, Rosenau, & Kosma, 2006) The carbonyl profiles (Fig 3, A, B) of both EK and BS reference ‘ozone’ pulps display the highest carbonyl group content in the low-Mw region This is due to O = oxygen delignification; EBI = electron beam irradiation stage; A = hot sulfuric acid stage; A(hot) = A-stage with increased temperature; E = alkaline extraction stage; Z = ozone stage; P = hydrogen peroxide stage ăpcke, Ibarra, & Ek, 2008; Miao et al., 2015) Finally, the et al., 2018; Ko peroxide stage (P) required an increased proportion of alkali to compensate for β-elimination reactions due to the higher number of keto groups from EBI and ozone stages The final IVs of EK-mixed, EK-ozone and BS-EBI were within the 450–500 mL g− target, while EK-EBI, BS-mixed, and BS-ozone delivered lower values, which allows the EBI or ozone doses to be lowered in those cases (Fig 1) Carbohydrate release was monitored by measuring the sugar composition of crude bleaching filtrates, both before and after total hydrolysis, to differentiate monomeric and polymeric fragments, respectively (Fig 2) EBI is known to release predominately oligomeric and polymeric hemicelluloses from the pulp (Sarosi et al., 2020) The extent of hemicellulose release is roughly correlated to the pulps’ hemicellulose content and to the irradiation dose Acid and ozone stages released minimal amounts of polymeric cellulose and hemicellulose with the exception of EK-ozone (Fig 2, E), which shows cellulose degradation to the monomer level, likely due to its highest ozone dose and longest dwell time in the reactor at acidic conditions During hydrogen peroxide bleaching, the alkaline conditions facilitate removal of low-molecular fragments, which mostly consist of hemicellulose Overall yield loss during bleaching, calculated as total sugar outflow from the pulp, was lowest in BS pulps, with values slightly above 0.1 %, Fig IV of eucalyptus kraft (A) and beech sulfite (B) pulps after EBI, hot acid, incremental ozone, or hydrogen peroxide stages, respectively Error bars correspond to 1.0 % inherent standard error of the method O.P Sarosi et al Carbohydrate Polymers 265 (2021) 118037 Fig Progressive sugar release from all bleaching stages of eucalyptus kraft and beech sulfite pulps Bleaching filtrates were analyzed before and after total hydrolysis, to differentiate between monomeric and polymeric carbohydrates, respectively A = EK-EBI; B = BS-EBI; C = EK-mixed; D = BS-mixed; E = EK-ozone; F = BS-ozone the overwhelming generation of REG in low-Mw fragments, which is also reflected in a larger fraction of DP < 200 species Oxidation of REG in the low-Mw region to carboxylic acid and lactone species, which are not covered by CCOA labelling, was secondary, as the carbonyl profiles of “ozone” variants indicated more carbonyl groups than “EBI” and “mixed” in that area The IV reduction caused by the P-stage is greater in EBI variants due to the facilitated backbone carbonyl formation in the high-Mw region Chain cleavage through β-elimination was shown to have a greater effect on IV if the keto group is located on a long chain than on a short chain In ΔDSCO (degree of carbonyl substitution including REG) plots (Fig 3, C, D) the respective CCOA signals of pulps from ‘EBI’ and ‘mixed’ treatment routes were subtracted from the signal of the conventional “ozone” variants to compare the oxidation profiles caused by each O.P Sarosi et al Carbohydrate Polymers 265 (2021) 118037 Table Sugar release data of each individual bleaching stage of eucalyptus kraft and beech sulfite pulps *Measured values were lower due to formation of hydrox ymethylfurfural during total hydrolysis Pulps EK-EBI EK-mixed EK-ozone BS-EBI BS-mixed BS-ozone Stage Cellulose monomeric (mg odgp− 1) Cellulose polymeric (mg odgp− 1) Hemicellulose monomeric (mg odgp− 1) Hemicellulose polymeric (mg odgp− 1) EBI A P EBI A Z P Ahot Z P EBI P EBI Z P Z P 0 0 0 59 64 0 126 0 116 35 0 58 34 5606 467 1987 3151 522 498 3838 0 326 7879 163 10 0 122 109 7879* 298 21 98 15 24 220 26 221 207 100 94 15 21 855 8535 519 519 544 77 690 114 800 Table CCOA data of all final pulps Pulps Mn (kg mol− 1) Mw (kg mol − ) Mz (kg mol− 1) DP< 100 (%) DP< 200 (%) DP< 2000 (%) DP> 2000 (%) Ð IV (mL g− 1) REG (μmol g− 1) C = O (μmol g− 1) EK-EBI EK-mixed EK-ozone BS-EBI BS-mixed BS-ozone 58 59 45 50 37 36 227 246 254 295 259 245 534 639 850 753 838 738 6 10 10 11 11 10 11 7 61 61 57 56 59 59 22 24 22 30 24 23 3.9 4.2 5.6 5.9 7.1 6.7 561 595 611 685 620 595 17.2 17.0 22.2 19.9 27.3 27.5 11.7 10.9 17.5 20.1 21.1 28.4 REG = reducing end groups; IV = intrinsic viscosity; DP = degree of polymerization; Mn, Mw or Mz = number, weight or z-average molecular mass approach As indicated by the absolute carbonyl group contents (Table 4), progressive replacement of ozone by EBI for IV control lead to a lower carbonyl group profile throughout the MWD The low-Mw region showed the strongest differences with ozone-treated pulps featuring more REG due to aforementioned diffusion limitations Only BS-EBI shows a moderately higher carbonyl group content than BS-ozone around a log(Mw) of ~3.8 In bleaching sequences with combined treatments of ozone and hydrogen peroxide, a greater number of carbonyl groups disappears through oxidation of REGs than in sequences with lower or without ozone stages Yet, the higher number of total carbonyl groups of reference “ozone” pulps permits the conclusion that “mixed” and “EBI” variants exhibit a lower amount of true cellulose backbone oxidation and thus better brightness stability (Ahn et al., 2019) resistant with R10 and R18 fractions on average 1.7 % and 0.4 % higher, respectively, than the other two BS variants Due to the sparse avail ability of data in the literature on alkali-resistance of pulps after EBI, one must consider other means of determining alkali-resistance, such as measuring the α-cellulose content (Ritter, 1929) Other researchers have found an exponential decrease in the α-cellulose content of sugarcane bagasse of up to 80 % by EBI with a dose of up to 40 kGy (Ribeiro, Oikawa, Mori, Napolitano, & Duarte, 2013) Such behavior was not indicated in the present results Another study suggested that γ-irradi ation in doses of up to 10 kGy had no effect on the α-cellulose content of bamboo paper kraft pulp, with minor reductions at 30 kGy and strong reductions beyond that irradiation level (Yang et al., 2010) Generally, an increasing level of irradiation causes polymeric chain length to fall below the dissolution limit in 10 % or 18 % NaOH, respectively How ever, at the given irradiation levels in both EK and BS pulps, the bulk of holocellulosic chain length remained above the dissolution limit in both EK and BS pulps at the given irradiation levels 3.2.2 Alkali-resistance R10 and R18 Pulp alkali-resistance in 10 % (R10) or 18 % (R18) NaOH showed distinct differences between each treatment variant (see supplementary information) Cellulose chain cleavage inevitably leads to a decrease in the R10 and R18 fractions However, since EBI statistically favors longer chains and ozone is diffusion-limited to outer areas for the fiber, the alkali-resistance of the “EBI” variant is less compromised than in the “ozone” pulp This is indicated by the MWD (Fig 3, A, B), where pulps with EBI displayed lower Ð and less shifts towards dissolution limits in 10 % and 18 % NaOH, respectively However, EK-EBI and EK-ozone display equal R10 and R18 fractions with EK-mixed having high R10 and R18 fractions with on average 2.2 % and 1.3 % higher values, respectively, than the other two BS-mixed had similar R10 and R18 values to BS-ozone due to their equal ozone stages and the low irradi ation dose of the former Hence, the behavior of those pulps during alkalization and viscose making may be the same BS-EBI is more alkali- 3.2.3 Pulp sugar composition The sugar composition of the final pulps (Fig 4, Table 5) was very similar within each group of EK or BS variants This is reasonable, since the yield loss of all treatment sequences was below 1.8 % Marginal differences were observed in the EK series, where xylan content decreased from 17.1 % in EK-ozone over 17.0 % in EK-mixed to 16.7 % in EK-EBI, but glucose recovery decreased in the same order from 80.3 % over 79.9 % to 78.9 %, respectively These small differences can be ascribed to side reactions such as formation of furfural and HMF during sample preparation Compared to the respective starting material, EK pulps lost between 1.8–2.2 % of hemicellulose content, while BS did not a show significant reduction (Table 1) The pulp crystallinity index of all pulps was 54.7–55.9 % and 54.0–54.5 % for EK and BS pulps, O.P Sarosi et al Carbohydrate Polymers 265 (2021) 118037 Fig Molecular weight distribution and carbonyl group profiles of eucalyptus kraft (A) and beech sulfite (B) pulps from variable treatments and their respective differential carbonyl group profiles Vertical lines R10 and R18 represent the lower limit of alkali resistance in 10 % or 18 % NaOH solution, respectively ΔDS plots are generated by subtracting the CCOA signal of ‘EBI’ or ‘mixed’ from the reference ‘ozone’ pulp signal, which shows the divergence of carbonyl group profiles within EK (C) and BS (D) pulps, respectively respectively, with differences between the treatment-variants well below the relative standard deviation If pulp crystallinity can be assumed as one indicator for pulp reactivity, differences of the latter between the pulps may be minimal (Ferreira, Evtuguin, & Prates, 2020) While reactivity measurements according to Fock or Treiber were not possible in the current study, other researchers have provided detailed insight A study by Gondhalekar et al found that crystallinity of a hardwood dissolving pulp was decreased by up to 9% and reactivity was increased by 11 % at a dose of kGy (Gondhalekar, Pawar, & Dhumal, 2019) Based on this data, reactivity changes by EBI can be assumed to be equal to those by ozone treatments 3.2.4 Degree of bleaching (DoB) The pulps’ DoB was quantified by kappa number and ISO brightness measurements (Fig 5) Out of the EK pulps, only EK-ozone with the conventional sequence reached brightness values that meet dissolving pulp specifications BS-mixed and BS-ozone showed similar and high DoB due to their equal Z-stage EK-EBI, EK-mixed and BS-EBI showed DoB below dissolving pulp specifications due to a lack of sufficient chromophore removal or destruction EBI at the employed doses does not introduce enough disruptions in the extended π-electron system of lignin and other chromophores to have an effect on pulp brightness (Sarosi et al., 2020) In contrast with cellulose, lignin shows good radical stabilization and is resistant against lower irradiation doses and thus remains mostly intact in the pulp after irradiation (Dizhbite, Telysheva, Jurkjane, & Viesturs, 2004; Faustino, Gil, Cecília, & Duarte, 2010) While EBI is known to form reactive oxygen species in atmospheric oxygen and water, such as ozone, peroxyl and hydroxyl radicals, the amount of generated bleaching agents in moist pulps is too low to have a Fig Total hydrolysis sugar composition of final eucalyptus kraft and beech sulfite pulps with variable bleaching sequences Table Data of total hydrolysis sugar composition of final eucalyptus kraft and beech sulfite pulps Pulps Glucose (%) Xylose (%) Mannose (%) Galactose (%) EK-EBI EK-mixed EK-ozone BS-EBI BS-mixed BS-ozone 78.9 79.9 80.3 94.8 94.7 94.3 16.7 17.0 17.1 2.7 2.7 2.7 0.1 0.1 0.1 0.8 0.7 0.7 0.2 0.2 0.2 0.0 0.0 0.0 O.P Sarosi et al Carbohydrate Polymers 265 (2021) 118037 REG in SX are not labeled by CCOA, and the calculated number of REG is more than double the total number of measured carbonyl groups, regardless if Mn or Mw is used for calculation Overall, isolated xylan is more resistant to degradation by EBI than cellulose pulp However, as shown by the sugar analysis of wash filtrates after irradiation (Fig 2), xylan is primarily leached from the pulps This may indicate that xylan Mw decreases barely below the dissolution limit after EBI, or that the accessibility of xylan fibers otherwise recalcitrant to dissolution is improved by EBI 3.4 The influence of EBI on HexA The kappa number of EK pulps may be partially impacted by HexA, which is attached to the xylan side chains in kraft pulps (Jiang et al., 2000; Vuorinen, Fagerstră om, Buchert, Tenkanen, & Teleman, 1999) As shown before, EK contains considerable amounts of xylan This gave rise to a small series of experiments in which a HexA-rich birch kraft pulp was irradiated The birch pulp was fully bleached, yet had a distinct yellow hue caused by the high HexA content The HexA content was traced using three methods: regular kappa measurements, uronic acid groups by the FDAM method, and HexA quantification based on the available TAPPI standard (Bohrn et al., 2006; TAPPI, 2007) Fig shows that EBI causes a linear increase of uronic acid groups at elevated irradiation doses, which is analogous to the carbonyl group formation found in other studies (Bouchard et al., 2006; Henniges et al., 2012) As has been shown, kappa numbers decrease with increasing irradiation doses (Sarosi et al., 2020) While the previous data showed a marginal kappa increase at elevated irradiation doses due to carbonyl group formation, it was not observed here Similar to other parameters like cellulose Mw or kappa number, the HexA content was reduced rapidly at low irradiation doses, with a leveloff effect at elevated doses In the dose range of 5–10 kGy, relevant for paper pulp upgrade, the HexA content was reduced by 10–26 %, while the highest reduction of 49 % was observed at a dose of 50 kGy HexA removal by EBI gives rise to improved pulp brightness stability, since HexA is known as a precursor for multiple chromophores (Rosenau et al., 2017) HexA content reduction is caused either by chemical modification or by removal of hemicelluloses Hemicellulose degrada tion by EBI to soluble fragments is observed, although the degree of hemicellulose removal can only account for a small part of the decrease in HexA content (Chen et al., 2016; Ribeiro et al., 2013) Interestingly, HexA content saw a slight increase at 200 kGy indicating the formation of double bonds, which are sensitive for analysis, at elevated irradiation doses Since HexAs react with potassium permanganate during kappa determination, they are considered “false lignin,” the extent of which can be calculated (Vuorinen et al., 1999) To determine that fraction, both variables, HexA content and Kappa number, were transformed into permanganate molar equivalents The KMnO4 consumption was directly taken from kappa measurements and a 1:1 ratio was used for calculating KMnO4 equivalents from the HexA concentration (Table 7) (Chai et al., 2001) Results indicate that up to one third of the kappa number is caused by HexAs The “false lignin” fraction decreases with irradiation, which indicates that HexAs are more susceptible to degradation by EBI than lignin, which is reasonable considering the structure and radical scavenging activity of the latter (Dizhbite et al., 2004) Fig Kappa number and brightness of eucalyptus kraft and beech sulfite pulps after their respective treatments Vertical lines represent the upper kappa limit of 1.0 and lower brightness limit of 90 % that are recognized as typical for dissolving pulps Error bars indicate the inherent standard error of the kappa (5%) and brightness (0.2 %) measurement method, respectively great effect on kappa number or brightness at the given dose (Cleland & Galloway, 2015; Gehringer, 1997; Sarosi et al., 2020) Since the “mixed” variant of each pulp gave a significantly higher DoB compared to the “EBI” route, especially in the case of EK pulp, a hybrid use of EBI and ozone in paper pulp upgrade is at least plausible, if the hemicellulose fraction is removed and the bleaching intensity is adjusted accordingly 3.3 The influence of EBI on isolated xylan EBI of isolated hemicellulose has rarely been investigated in previous studies (Chen et al., 2016; Ma et al., 2014) Isolating xylan before irra diation may reveal effects that are otherwise overshadowed by the presence of cellulose Hence, both isolated eucalyptus kraft xylan (KX) and beech sulfite xylan (SX) were irradiated and analyzed by the CCOA method The Mw reduction of xylan was less pronounced than for cellulosic components since the fragment size was already low (Table 6) Non-irradiated KX had a relatively high Mw, which was reduced to almost level-off Mw after a dose of just 10 kGy, while SX was barely affected by EBI (Table 6) Other researchers have observed a similar resistance of the Mw of hemicellulose towards irradiation (Ma et al., 2014) The MWD of KX showed peak broadening at high irradiation levels, which may indicate the simultaneous occurrence of chain cleavage and cross-linking, with the former being more pronounced (Fig 6) Carbonyl group content increased moderately for SX and strongly for KX at high irradiation doses In the latter case, a significant part of the carbonyl groups originate from newly formed REG The majority of REG groups of SX are oxidized since it originates from an acidic magnesium bisulfite process Therefore, a significant portion of Table Weight average molecular mass, carbonyl group content and calculated REG of eucalyptus kraft and beech sulfite xylan after irradiation at varying doses Mw (kg mol− 1) Carbonyl group content (μmol g− 1) REG calculated from Mn (μmol g− 1) REG calculated from Mw (μmol g− 1) Sample kGy 10 kGy 100 kGy 200 kGy KX SX KX SX KX SX KX SX 47.6 5.5 71.6 67.8 25.8 183.2 21.0 156.0 14.4 4.9 66.1 69.5 87.2 202.4 69.3 154.6 11.9 4.4 89.3 82.7 83.8 228.8 83.8 186.9 13.0 4.6 216.1 84.7 160.5 218.8 77.2 180.5 Conclusion In the present study, a eucalyptus kraft paper pulp and a beech sulfite dissolving pulp were subjected to different bleaching sequences, con sisting of either an EBI, an ozone stage, or a combination of both, with the aim of lowering the IV to levels applicable for RCF processes Overall yield loss of the sequences measured by carbohydrate outflow was around 0.1 % for all beech dissolving pulps, 0.8 % for EK-EBI and EKmixed pulps and 1.8 % for EK-ozone pulp EBI posed a tool for REG = reducing end groups O.P Sarosi et al Carbohydrate Polymers 265 (2021) 118037 Fig Molecular weight distribution and carbonyl group profiles of eucalyptus kraft (A) and beech sulfite (B) xylan after irradiation at varying dose displayed the highest alkali-resistance out of all tested pulps, high uni formity, the lowest carbonyl group content, a suitable IV, and a bleaching degree slightly below dissolving pulp specifications On the other hand, acid sulfite pulping generates a pulp that already has a low IV, making the use of EBI for IV control less important, despite similar dispersity and oxidation advantages EBI is a suitable treatment method for IV reduction of high-Mw pulps, which can be used to substitute otherwise intensive chemical treatments and release potential process bottlenecks However, since EBI had no significant effect on lignin at the employed irradiation levels, pulps with EBI-only sequences suffered from low bleaching degrees Herein, the combined use of EBI and ozone posed a good compromise, unifying advantages of both treatments Additional irradiation experiments on HexA-rich birch pulp and isolated xylan samples revealed a reduction of the former of up to 49 % EBI by a dose of 50 kGy While xylan sample’s Mw were barely above or within lower level-off regions, the degree of oxidation increased moderately for beech sulfite xylan and strongly for eucalyptus kraft xylan Overall, changes imparted in xylan by EBI are weaker than in cellulose pulps at equal irradiation doses, especially if the xylan Mw is already low Fig Birch pulp HexA content, uronic acid content, and kappa values after EBI with varying dose CRediT authorship contribution statement Oliver P Sarosi: Conceptualization, Investigation, Data analysis, Writing - original draft Daniela Bammer: Investigation Elisabeth Fitz: Writing - review & editing, Supervision Antje Potthast: Concep tualization, Data analysis, Manuscript review & editing, Supervision Table Permanganate equivalent concentrations of irradiated birch pulp calculated from Kappa number or HexA measurements and the fraction of “false lignin” caused by HexAs *The 1.25 kGy sample was determined as an outlier in both kappa and HexA measurements due to irregularities during measurements Irradiated birch pulp sample KMnO4 equivalent “Kappa” (μmol g− 1) KMnO4 equivalent “HexA” (μmol g− 1) Fraction of “false lignin” caused by HexA (%) Reference 1.25 kGy* 2.5 kGy 5.0 kGy 10.0 kGy 50.0 kGy 100 kGy 200 kGy 60.9 42.1* 65.0 64.1 57.7 53.2 51.2 50.3 21.9 18.5* 21.4 19.7 16.2 11.5 11.1 15.1 36.0 44.0* 32.8 30.8 28.0 21.5 21.7 30.0 Funding This research was funded by the Austrian Research Promotion Agency (FFG), Grant Number 844608 Open access was supported by BOKU Vienna Open Access Publishing Fund Declaration of Competing Interest The authors report no conflict of interests Acknowledgements efficient IV reduction, giving rise to a potential use in upgrading high-IV paper pulps to dissolving pulps The CCOA measurements supported this hypothesis, revealing a lower carbonyl group content and improved carbonyl profiles when progressively replacing the ozone stage with EBI Additionally, EBI-treated variants had a lower dispersity of molar masses and a smaller shift towards the low-Mw region due to the sta tistically high chance of cleaving long chain cellulose, which is prefer able for dissolving pulp This was also expressed by higher alkaliresistant fractions R10 and R18 in EBI-treated pulps “EK-mixed” pulp Financial support was provided by the Austrian government and by the provinces of Lower Austria, Upper Austria and Carinthia, as well as by Lenzing AG We also express our gratitude to the University of Nat ural Resources and Life Sciences (BOKU), Vienna and Lenzing AG for their in-kind contributions Furthermore, we thank the responsible project manager at Lenzing AG Robert Bischof Last but not least, special thanks to all lab technicians for their patience and laboratory support, especially Sonja Schiehser and Markus Huemer O.P Sarosi et al Carbohydrate Polymers 265 (2021) 118037 Appendix A Supplementary data Henniges, U., Okubayashi, S., Rosenau, T., & Potthast, A (2012) Irradiation of cellulosic pulps: Understanding its impact on cellulose oxidation Biomacromolecules, 13(12), 4171–4178 https://doi.org/10.1021/bm3014457 Hutterer, C., Kliba, G., Punz, M., Fackler, K., & Potthast, A (2017) Enzymatic pulp upgrade for producing high-value cellulose out of a Kraft paper pulp Enzyme and Microbial Technology, 102(7), 67–73 https://doi.org/10.1016/j enzmictec.2017.03.014 Hutterer, C., Schild, G., & Potthast, A (2016) A precise study on effects that trigger alkaline hemicellulose extraction efficiency Bioresource Technology, 214, 460–467 https://doi.org/10.1016/j.biortech.2016.04.114 Jiang, Z H., Lierop, B., & Robson, B (2000) Hexenuronic acid groups in pulping and bleaching chemistry Tappi Journal, 83(1), 167–175 https://doi.org/10.1016/j biortech.2013.01.049 Kang, G., Zhang, Y., Ni, Y., & van Heiningen, A R P (1995) Influence of lignins on the degradation of cellulose during ozone treatment Journal of Wood Chemistry and Technology, 15(4), 413–430 https://doi.org/10.1080/02773819508009518 Kishimoto, T., & Nakatsubo, F (1998) Non-chlorine bleaching of kraft pulp V Participation of radical species in ozonation of methyl 4-O-ethyl--Dglucopyranoside Holzforschung, 52(2), 185 https://doi.org/10.1515/ hfsg.1998.52.2.185 Kă opcke, V., Ibarra, D., & Ek, M (2008) Increasing accessibility and reactivity of paper grade pulp by enzymatic treatment for use as dissolving pulp Nordic Pulp and Paper Research Journal, 23(4), 363–368 https://doi.org/10.3183/npprj-2008-23-04-p363368 Kubes, G J., Fleming, B I., Macleod, J M., Bolker, H I., & Werthemann, D P (1983) Viscosities of unbleached alkaline pulps II The G-factor Journal of Wood Chemistry and Technology, 3(3), 313333 https://doi.org/10.1080/02773818308085166 Kvarnlă of, N., Să oderlund, C A., & Germgård, U (2006) The effect of modifying the oxidative pre-aging conditions in the manufacture of viscose from wood pulp Paperi Ja Puu, 88(3), 175–180 Lachenal, D., Mishra, S., & Chirat, C (2013) The effect of introducing ozone in elemental chlorine free bleaching of eucalyptus kraft pulp Pulp Tappi Journal, 12(11), 39–45 https://doi.org/10.32964/tj12.11.39 Lundberg, V., Axelsson, E., Mahmoudkhani, M., & Berntsson, T (2012) Energy analysis for conversion of a kraft pulp mill into a dissolving pulp mill Chemical Engineering Transactions, 29, 13–18 Ma, X., Zheng, X., Zhang, M., Yang, X., Chen, L., Huang, L., et al (2014) Electron beam irradiation of bamboo chips: Degradation of cellulose and hemicelluloses Cellulose, 21(6), 3865–3870 https://doi.org/10.1007/s10570-014-0402-4 Miao, Q., Tian, C., Chen, L., Huang, L., Zheng, L., & Ni, Y (2015) Combined mechanical and enzymatic treatments for improving the Fock reactivity of hardwood kraft-based dissolving pulp Cellulose, 22(1), 803–809 https://doi.org/10.1007/s10570-0140495-9 Mozdyniewicz, D., Nieminen, K., & Sixta, H (2013) Alkaline steeping of dissolving pulp Part I: Cellulose degradation kinetics Cellulose, 20, 1437–1451 https://doi.org/ 10.1007/s10570-013-9926-2 Ni, Y., Kang, G J., & van Heiningen, A R P (1996) Are hydroxyl radicals responsible for degradation of carbohydrates during ozone bleaching of chemical pulp? Journal of Pulp and Paper Science, 22(2), 53–57 Potthast, A., Rosenau, T., & Kosma, P (2006) Analysis of oxidized functionalities in cellulose In D Klemm (Ed.), Polysaccharides II (pp 1–48) Berlin, Heidelberg: Springer Berlin Heidelberg Pouyet, F., Chirat, C., Potthast, A., & Lachenal, D (2014) Formation of carbonyl groups on cellulose during ozone treatment of pulp: Consequences for pulp bleaching Carbohydrate Polymers, 109, 85–91 https://doi.org/10.1016/j.carbpol.2014.02.082 Ribeiro, M A., Oikawa, H., Mori, M N., Napolitano, C M., & Duarte, C L (2013) Degradation mechanism of polysaccharides on irradiated sugarcane bagasse Radiation Physics and Chemistry, 84, 115–118 https://doi.org/10.1016/j radphyschem.2012.06.034 Ritter, G J (1929) Determination of alpha-cellulose Industrial & Engineering Chemistry Analytical Edition, 1(1), 5254 https://doi.org/10.1021/ac50065a027 Ră oder, T., Moosbauer, J., Fasching, M., Bohn, A., Fink, H.-P., Baldinger, T., et al (2006) Crystallinity determination of native cellulose - comparison of analytical methods Lenzinger Berichte, 86, 132136 Ră ohrling, J., Potthast, A., Rosenau, T., Lange, T., Borgards, A., Sixta, H., et al (2002) A novel method for the determination of carbonyl groups in cellulosics by fluorescence labeling Validation and applications Biomacromolecules, 3(7), 969975 https://doi.org/10.1021/bm020030p Ră ohrling, J., Potthast, A., Rosenau, T., Lange, T., Ebner, G., Sixta, H., et al (2002) A novel method for the determination of carbonyl groups in cellulosics by fluorescence labeling Method development Biomacromolecules, 3(5), 959–968 https://doi.org/10.1021/bm020029q Rosenau, T., Potthast, A., Zwirchmayr, N S., Hettegger, H., Plasser, F., Hosoya, T., et al (2017) Chromophores from hexeneuronic acids: Identification of HexA-derived chromophores Cellulose, 24(9), 3671–3687 https://doi.org/10.1007/s10570-0171397-4 Sappi Limited (2013) Sappi fine paper North America announces successful completion of $170M major capital investment in North American operations Accessed Date: 19 May 2020, Retrieved from https://www.sappi.com/de/node/874 Sarosi, O P., Bischof, R H., & Potthast, A (2020) Tailoring pulp cellulose with Electron beam irradiation: Effects of lignin and hemicellulose ACS Sustainable Chemistry & Engineering, 8(18), 7235–7243 https://doi.org/10.1021/acssuschemeng.0c02165 Sixta, H (2006) Prehydrolysis Handbook of pulp (pp 325–345) Weinheim: Wiley-VCH Sixta, H., Andrea, P., & Kraft, G (2007) Method for producing cellulose Patent No.: WO2007128027A1 Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.carbpol.2021.118037 References Agarwal, N., & Gustafson, R (1997) A contribution to the modeling of kraft pulping The Canadian Journal of Chemical Engineering, 75, 8–15 https://doi.org/10.1002/ cjce.5450750104 Ahn, K., Zaccaron, S., Zwirchmayr, N S., Hettegger, H., Hofinger, A., Bacher, M., et al (2019) Yellowing and brightness reversion of celluloses: CO or COOH, who is the culprit? Cellulose, 26(1), 429–1444 https://doi.org/10.1007/s10570-018-2200-x Antes, R., & Joutsimo, O P (2015) Effect of modified cooking on bleachability of Eucalyptus globulus and Eucalyptus nitens Bioresources, 10(1), 597612 https:// doi.org/10.15376/biores.10.1.597-612 Berggren, R., Berthold, F., Sjă oholm, E., & Lindstră om, M (2001) Fiber strength in relation to molecular mass distribution of hardwood kraft pulp Nordic Pulp and Paper Research Journal, 16(4), 333–338 https://doi.org/10.3183/npprj-2001-16-04-p333338 Bohrn, R., Potthast, A., Schiehser, S., Rosenau, T., Sixta, H., & Kosma, P (2006) The FDAM method: Determination of carboxyl profiles in cellulosic materials by combining group-selective fluorescence labeling with GPC Biomacromolecules, 7, 1743–1750 https://doi.org/10.1021/bm060039h Bouchard, J., M´ethot, M., & Jordan, B (2006) The effects of ionizing radiation on the cellulose of woodfree paper Cellulose, 13(5), 601–610 https://doi.org/10.1007/ s10570-005-9033-0 Brogdon, B (2009) A fundamental review and critical analysis of hexenuronic acids and their impact in elemental chlorine-free bleaching 2009 TAPPI engineering, pulping an environmental conference Burkart, P (1999) Cellulose Activation of dissolving pulp by electron beam irradiation A new route to a safer and more profitable viscose process Polymer News, 24(6), 194–197 Chai, X.-S., Zhu, J., & Li, J (2001) A simple and rapid method to determine hexeneuronic acid groups in chemical pulps Journal of Pulp and Paper Science, 27, 165–170 Chen, J., Wang, L., Su, X., Wang, K., Wu, X., Chen, L., et al (2016) Structure, morphology, thermostability and irradiation-mediated degradation fractions of hemicellulose treated with γ-irradiation Waste and Biomass Valorization, 7(6), 1415–1425 https://doi.org/10.1007/s12649-016-9489-1 Chen, Q.-Y., Ma, X.-J., Li, J., Miao, Q., & Huang, L (2017) Effect of the utilization of electron beam irradiation on the reactivity of bamboo dissolving pulp Bioresources, 12(3), 6251–6261 https://doi.org/10.15376/biores.12.3.6251-6261 Cleland, M R., & Galloway, R A (2015) Ozone generation in air during electron beam processing Physics Procedia, 66, 586–594 https://doi.org/10.1016/j phpro.2015.05.078 Dizhbite, T., Telysheva, G., Jurkjane, V., & Viesturs, U (2004) Characterization of the radical scavenging activity of lignins––natural antioxidants Bioresource Technology, 95(3), 309–317 https://doi.org/10.1016/j.biortech.2004.02.024 Duan, C., Verma, S K., Li, J., Ma, X., & Ni, Y (2016) Combination of mechanical, alkaline and enzymatic treatments to upgrade paper-grade pulp to dissolving pulp with high reactivity Bioresource Technology, 200, 458–463 https://doi.org/ 10.1016/j.biortech.2015.10.067 Faustino, H., Gil, N., Cecília, B., & Duarte, A (2010) Antioxidant activity of lignin phenolic compounds extracted from kraft and sulphite black liquors Molecules, 15, 9308–9322 https://doi.org/10.3390/molecules15129308 Ferreira, J C., Evtuguin, D V., & Prates, A (2020) Effect of cellulose structure on reactivity of eucalyptus acid sulphite dissolving pulp Cellulose, 27(8), 47634772 https://doi.org/10.1007/s10570-020-03092-y ă Gehringer, P (1997) Radiation processing of aqueous systems (pp 1–5) Seibersdorf: OFZS, ¨ Osterreichisches Forschungszentrum Seibersdorf GlobeNewswire (2020) Amid the COVID-19 crisis and the looming economic recession, the Cellulosic Man-Made Fibers market worldwide will grow by a projected 2.2 Million Tons, during the analysis period Accessed Date: 27 January 2021, Retrieved from https ://www.globenewswire.com/news-release/2020/06/03/2043336/0/en/Amid-the -COVID-19-crisis-and-the-looming-economic-recession-the-Cellulosic-Man-Made -Fibers-market-worldwide-will-grow-by-a-projected-2-2-Million-Tons-during-the -analysis-period.html Gomes, V J., Longue, D., Colodette, J L., & Ribeiro, R A (2014) The effect of eucalypt pulp xylan content on its bleachability, refinability and drainability Cellulose, 21(1), 607–614 https://doi.org/10.1007/s10570-013-0104-3 Gondhalekar, S C., Pawar, P J., & Dhumal, S S (2019) Use of electron beam irradiation for improving reactivity of dissolving pulp in viscose process Journal of Radioanalytical and Nuclear Chemistry, 322, 67–72 https://doi.org/10.1007/s10967019-06563-0 Hammer, B E., Christensen, N L., Conroy, M J., King, W J., & Pogue, N (2011) Penetration depth measurement of a MeV electron beam in water by magnetic resonance imaging Physical Review Special Topics Accelerators and Beams, 14, 11 He, T., Liua, M., & Tian, X (2018) Kinetics of ozone bleaching of eucalyptus kraft pulp and factors affecting the properties of the bleached pulp Bioresource Technology, 13 (1), 425–436 https://doi.org/10.15376/biores.13.1.425-436 Henniges, U., Hasani, M., Potthast, A., Westman, G., & Rosenau, T (2013) Electron beam irradiation of cellulosic materials—Opportunities and limitations Materials, (5), 1584–1598 https://doi.org/10.3390/ma6051584 10 O.P Sarosi et al Carbohydrate Polymers 265 (2021) 118037 Staehelin, J., Buehler, R E., & Hoigne, J (1984) Ozone decomposition in water studied by pulse radiolysis Hydroxyl and hydrogen tetroxide (HO4) as chain intermediates The Journal of Physical Chemistry, 88(24), 5999–6004 https://doi org/10.1021/j150668a051 TAPPI (2007) Hexenuronic acid content of chemical pulp (T 282 pm-07) Tripathi, S., Bhardwaj, N., & Ghatak, H (2018) Additives to decrease cellulose chain scission during ozone bleaching of wheat straw pulp Nordic Pulp and Paper Research Journal, 33(3), 430–438 https://doi.org/10.1515/npprj-2018-3048 Tsuji-Katsukawa, S., Miyawaki, S., & Koyanagi, T (2012) Development of a technique for removal of hexenuronic acid in ECF-bleached pulp using UV irradiation Kami Pa Gikyoshi, 66(3), 287–292 https://doi.org/10.2524/jtappij.66.287 Vuorinen, T., Fagerstră om, P., Buchert, J., Tenkanen, M., & Teleman, A (1999) Selective hydrolysis of hexenuronic acid groups and its application in ECF and TCF bleaching of kraft pulps Journal of Pulp and Paper Science, 25(5), 155–162 Yang, Y (2016) β-Elimination side reactions Side reactions in peptide synthesis (pp 33–42) Oxford: Academic Press https://doi.org/10.1016/B978-0-12-8010099.00002-1 Yang, G., Zhang, Y., Wei, M., Shao, H., & Hu, X (2010) Influence of γ-ray radiation on the structure and properties of paper grade bamboo pulp Carbohydrate Polymers, 81 (1), 114–119 https://doi.org/10.1016/j.carbpol.2010.02.003 Zhang, X Z., Ni, Y., & van Heiningen, A (2000) Kinetics of cellulose degradation during ozone bleaching Journal of Pulp and Paper Science, 26(9), 335–340 11 ... acids and their impact in elemental chlorine-free bleaching 2009 TAPPI engineering, pulping an environmental conference Burkart, P (1999) Cellulose Activation of dissolving pulp by electron beam irradiation. .. previous studies, since EBI is known to randomly cleave the cellulose chain, which is expressed by a linear increase of the number of chain scissions and an exponential decrease of IV and weight average... as hemicellulose and lignin, towards chain scission and oxidation were investigated (Sarosi et al., 2020) Hemicellulose was found to protect cellulose from chain scission and backbone oxidation,