Fusarium concolor X4 Pretreatment Suppresses Light-Induced Yellowing of High-Yield Pulp

High-yield pulps (HYPs), such as CTMP (chemi-thermo-mechanical pulp), are attractive due to their low cost and high wood utilization. However, their drawback of rapid brightness reversion (yellowing) limits wide use of the HYPs. In this study, a fungus, Fusarium concolor X4, was applied to treat poplar CTMP for exploring the effects of biotreatment on brightness and light-induced yellowing of the pulp. The results indicated that the biotreatment with Fusarium concolor X4 could improve the brightness of poplar CTMP and inhibit light-induced yellowing of the pulp. The yellowing inhibition mechanism was explored by the analysis of enzyme production regularity during biotreatment, changes in chemical components, and the UV-Vis absorption spectra and FTIR-ATR spectra of pulps before and after biotreatment.

A STUDY OF THE PHYSICO-MECHANICAL PROPERTIES IN SHORT BLEACHING SEQUENCES

ABSTRACT The kraft pulp of Eucalyptus spp. is relatively easy to be bleached. Therefore, studies have been carried out to reduce the number of stages of bleaching in the plant and minimize process costs. The present work aimed to evaluate the use of two short bleaching sequences in the physico-mechanical properties of cellulosic pulp as well as to compare these values to the ones obtained by usual bleaching sequences. The four bleaching sequences were ECF (elemental chlorine free), D0(E+P)D1P, AHTD0(E+P)D1P, and AHTDP and AHTD (PO). For each bleaching sequence the brightness, brightness reversion and total cost of reagents were evaluated. Physical and mechanical analyses were performed according to the methodologies of the Technical Association of the Pulp and Paper Industry (TAPPI, 2002). The AHTD (PO) sequence showed higher brightness, less brightness reversion, lower total cost and better smoothness compared to the reference sequences. However, it had a lower tear index and a lower compression index. The AHTDP sequence did not reach target brightness, however, it presented brightness reversion and lower total cost than the reference sequences. The AHTDP sequences showed high compression and smoothness, but presented a low compression index.

Brightness stability of eucalyptus-dissolving pulps: effect of the bleaching sequence

The factors governing the brightness reversion (BR) of dissolving pulps under heat exposure are investigated. Carbonyl (CO) groups were artificially introduced on fully bleached pulp by sodium hypochlorite (NaClO) oxidation. It was demonstrated that the CO groups are responsible for loss of brightness stability (BS). These groups were partly eliminated by an alkaline extraction stage (E), which improved BS. However, an alkaline peroxide stage (P) was more efficient than E to improve BS, but without any additional CO loss. Moreover, an unbleached dissolving pulp was bleached in the laboratory by elemental chlorine free (ECF) and totally chlorine free (TCF) [ozone-based] sequences to the same brightness. The very low CO content was about the same in both cases. The ECF-bleached pulp showed substantially lower BS than the TCF pulp. These results are interpreted such that the chemistry of chromophores in the unbleached pulp also governs BS. In situ detection of phenolic and quinone chromophores in bleached dissolving pulp was performed by electron paramagnetic resonance (EPR) spectroscopy and ultraviolet resonance Raman (UVRR) spectroscopy. The content of these groups was bleaching-sequence-dependent, which may be related to the BS differences.

Reactions between peracetic acid and lipophilic extractives – methodologies and implications in post bleaching of kraft pulps

Pulp mills constantly look for opportunities to increase their production capacity without major investments, as well as to save in overall bleaching costs. Peracetic acid (PAA) is used in post bleaching of kraft pulps to increase pulp brightness, to prevent brightness reversion in pulp storage, and to prohibit problems caused by extractives. However, the rates and significance of reactions between PAA and lipophilic extractives in pulp bleaching are not known in detail. Hence, the reactions between PAA and model compounds of extractives have been studied as emulsions in water and directly in methyl-tert-butyl ether (MTBE). Unsaturated compounds were found to be reactive in both water and MTBE, and the conventional extractive analyses had to be modified. Freeze-drying the reaction mixture with subsequent trimethylsilylation and GC-analysis was a very effective analytical approach. As a result of PAA treatment, fatty acids and sterols with double bonds were shown to form epoxides and the corresponding diols. Dehydroabietic acid (DeAb) also reacted with PAA by oxidation of the benzylic position. After longer reaction times, the reaction products of the extractives were further degraded or formed cross-linked aggregates. The epoxides and diols were also identified in samples from pulp mills applying PAA in post bleaching.

Ozone bleaching of South African Eucalyptus grandis kraft pulps containing high levels of hexenuronic acids

Ozone use in conjunction with chlorine dioxide during pulp bleaching offers several advantages over conventional bleaching sequences that make use of chlorine dioxide only. Despite this, in South Africa, only one mill uses ozone. The current study was a preliminary investigation into the use of ozone in bleaching sequences for kraft pulps produced from South African Eucalyptus grandis wood chips, which typically contained high amounts of hexenuronic acids (HexA). The objective of the study was to compare the performance of ozone to other technologies used to remove HexA, such as acid hydrolysis (A) and hot chlorine dioxide (DHT) stages. Bleaching sequences using chlorine dioxide (i.e., OAD0ED1D2 and ODHTED1D2) were compared to bleaching sequences using ozone (i.e., OZD0ED1 and OAZD0ED1). The results showed that ozone preferentially reacted with HexA in the presence of lignin. When applied after oxygen delignification, ozone had the same HexA removal efficiencies as the A- and DHT- stages at dosages in excess of 0.6%. When used in combination with the A-stage, the HexA removal efficiencies of ozone reached 96%. Consequently, up to 15% savings in the estimated bleaching chemical costs were achieved when the OAZD0(EP)D sequence was used, compared to the standard reference sequence (OAD0ED1D2). The residual HexA in the bleached pulp affected brightness reversion of the pulps, but this was only evident for the bleaching sequences that used chlorine dioxide, not for those that included ozone.

Prebleaching of eucalypt kraft pulp with OP stages: Effect of an acid pretreatment or chelation step

We conducted a comparative evaluation of different treatments for the bleaching of eucalypt kraft pulps beginning with OP stages. The treatments tested were (1) an acid chelation stage with DTPA (OQP sequence); (2) a hot acid stage (AOP sequence); and (3) a chelant addition into the alkaline oxygen stage ((OQ)P and A(OQ)P sequences). The latter strategy was also studied for environmental reasons, as it contributes to the closure of the filtrate cycle. The OQP sequence leads to the highest brightness gain and pulp viscosity and the lowest peroxide consumption caused by an efficient metals control. Considering that the low biodegradability of the chelant is a problem, the A(OQ)P sequence is an interesting option because it leads to reduced peroxide consumption (excluding OQP) while still reaching high brightness values and similar brightness reversion to OQP prebleaching, with only a viscosity loss of 160 dm3/kg. Therefore, a hot acid stage could be considered when a separate acid Q stage is absent in a prebleaching sequence of Eucalyptus globulus kraft pulps involving OP stages.

Assessment of pulp machine white water quality at market kraft pulp mills

The bleaching of pulp is a significant cost, yet the brightness achieved in the bleaching plant can be diminished in the pulp machine because of white water (WW) quality. Monitoring WW quality can control these losses. A method was developed to assess WW quality that allows differentiation between the effect of fibers, fines, and dissolved solids (DS) in the WW. It was found that the quality of the WW varied greatly from mill to mill. The brightness loss was mainly affected by the presence of fines, through a combination of their concentration and color. The DS were significantly less detrimental to the optical properties of the final furnish. None of the constituents present in the pulp machine WW caused significant brightness reversion (except the hardwood fine fractions). It is therefore recommended that a monitoring procedure for WW quality at the mill site be used to diagnose and prevent the occurrence of brightness problems. Such monitoring offers a way to reduce bleaching costs.

Bleaching in Paper Conservation

Chemical bleaches are powerful chemical agents that destroy colour by breaking and reforming covalent bonds within organic colouring matter. They are, consequently, the most potentially damaging chemicals used in paper conservation treatments and their use should only be considered when all other means of removing discolouration have been fully explored. The colour of organic compounds depends upon the presence of a number of multiple bonds linked together in a conjugated system known as a chromophore. Rupture of the conjugated system renders it colourless. This is the process that occurs in bleaching. Chemical bleaches may be either oxidising or reducing agents. The tendency of paper to yellow with age is know as brightness reversion. Lignin is an important source of colour, especially in regard to the yellowing of paper based on mechanical wood pulps. In non ligneous papers, yellowing is commonly associated with the oxidation of cellulose and associated materials, such as hemicelluloses, resulting in the formation of carbonyl groups. The most powerful oxidising bleaches are based on the hypochlorite ion, OClˉ, and include bleaching powder, sodium hypochlorite , calcium hypochlorite and chloramine-T. The preparation, chemical properties and use of these agents are discussed in detail. Attention is draw to the importance of keeping the pH above 9 during treatment. This is in order to minimise the formation of carbonyl groups. After bleaching with these agents, thorough washing and deacidification is recommended. The oxidising agent chlorine dioxide has certain advantages. However, in a conservation context, its use is highly questionable due to serious health and safety issues. Hydrogen peroxide is a moderate bleaching agent and its preparation, chemical properties and use are discussed in detail. Stabilising agents are recommended when using this bleach. Sodium borohydride is the only reducing agent commonly used in paper conservation. Not only is it an effective bleaching agent it also has the benefit of increasing paper stability by re-ducing the carbonyl groups present in oxidised cellulose. Its preparation, chemical properties and use are discussed in detail.

An Evaluation of Historical Bleaching with Chlorine Dioxide Gas, Sodium Hypochlorite, and Chloramine-T at the Fogg Art Museum

In the mid-twentieth century, drawings by Jean-Auguste-Dominique Ingres at the Fogg Art Museum were treated with chemical bleaches such as chlorine dioxide gas, sodium hypochlorite, and chloramine-T. Fifty years later, the darkened condition of the drawings was attributed to bleaching with chlorine dioxide gas. This paper discusses the three methods developed by Rutherford John Gettens to generate chlorine dioxide gas from sodium chlorite, formaldehyde and formic acid, examines the use of these bleaching methods to treat Ingres drawings at the Fogg, and discusses the sodium hypochlorite and chloramine-T bleaching methods also in use at the time. The treatments of two Ingres drawings are compared and evaluated in light of later bleaching studies and the current condition of each drawing. All of these historical bleaching methods, as practiced on the works studied, contributed to the darkening and colour/brightness reversion of drawings.