A literature survey on the various bleaching methods used on deinked stock and the factors which influence the fading characteristic of deinked stock is compiled. Mention is also made of various additives which have an influence on the fading of a sheet. A description of the experimental work with caustic deinked stack of various groundwood content follows. Results indicate that the groundwood content has more effect upon fading of deinked stock than the number of stages of bleaching, although the increase in the number of stages of bleaching does reduce the amount of fading in a sheet. A greater effect by the number of stages of bleaching is obtained in the higher groundwood range

Avery, Phillip H.

English

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Western Michigan University ScholarWorks at WMU Paper Engineering Senior Theses Chemical and Paper Engineering 6-1952 The Influence of Single, Two, and Three Stage Bleaching on Fading Characteristic of Deinked Stock Phillip H. Avery Western Michigan College Follow this and additional works at: https://scholarworks.wmich.edu/engineer-senior-theses  Part of the Wood Science and Pulp, Paper Technology Commons Recommended Citation Avery, Phillip H., "The Influence of Single, Two, and Three Stage Bleaching on Fading Characteristic of Deinked Stock" (1952). Paper Engineering Senior Theses. 98. https://scholarworks.wmich.edu/engineer-senior-theses/98 This Dissertation/Thesis is brought to you for free and open access by the Chemical and Paper Engineering at ScholarWorks at WMU. It has been accepted for inclusion in Paper Engineering Senior Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact maira.bundza@wmich.edu. The Influence of Single., Two,and Three Stage Bleachingon Fading Characteristic of Deinked Stock/• A senior Thesis submittedas a requirement in Pulpand Paper Technology at Western Michigan Collegel December 15, 1951.June 1, 1952 Phillip H. Avery1 -Index-Page Abstract------------------------------------------ 2 Literature Survey--------------------------------- 3 Introduction--------------------------------- 3 Various Bleaching Methods Used on------------ 3 Deinked Stock Fading Characteristics of De1nked------------ 4 Stock Experimental Work--------------------------------- 9Table I - Permanganate Number and------------ 9 , Equivalent Bleach Consumption of Deinked Stock Literature Cited---------------------------------- 13 Fig. I - Graft of De@ree of Fading vs------------- 14 Hours in Fade-Ometer 2 -Abstract-A literature survey on the various bleaching methods used on deinked stock and the factors whieh influence the fading characteristic of deinked stock is compiled. Mention is also made of various additives which have an influence on the fading of a sheet. A description of the experimental work whth caustic deinked stack of various groundwood con­tent follows. Results indicate that the groundwood content has more effect upon fading of deinked stock than the num­ber of stages of bleaching, although the increase in the number of s•ages of bleaching does reduce the amount of fading in a sheet. A greater effect by the number of stages of bleaching is obtained in the higher groundwood range. 3 7 Literature Survey Introduction The use of bleached deinked paper stock has increased greatly in the past years. Due to recent developnents in methods of deinking, washing, and bleaching, deinked stock can now be used in all but the finest grades of writing and record paper. This developnent in tech­no�ogical knowledge has not only eased greatly the strain on our forest reserves but has also developed an economical outlet for the use of a gigantic waste material. Various Bleaching Niethods Used .Q11J;)einked Stock Because of the non-uniformity of deinked stock and its similarity to cornnercial wood pulps very little has been written about the bleaching of deinked stock. The bleaching processes most used are single, two, and three stage with some peroxide and hydrosulphite bleaching being used if the groundwood content of the stock is high. These processes ' usually prove to be efficient to reach the required brightness of the stock and are identical with those used in commercial wood pulps. The composition of deinked stock varies considerably in groundwood content and initial brightness depending upon the raw materials used. Therefore, a manufacturer will have to build his particular bleaching system to fit the type of raw materials used and the final brightness desired. Even from batch to batch these initial characteristics of the stock vary considerably, so that his bleaching system must be a flexible one in order to cover the range of deviation in th� stoct, prepared. Some of the factors which influence the type of bleaching system 4 used are: initial costs, space required, volume of bleaching done, and degree of brightness desired. The single stage bleaching system uses a minimum amount of space, but the chemical costs are higher and the pulp is degraded more than in ..thetwo or three stage bleaching. In the two and three stage bleaching the yields are lower but the final brightness is higher and the chemical costs are lower. Peroxide and hydrosulphite do not attack the cellulose, but their costs are high. The use of sodium hypochlorite bleach has increased greatly despite the fact that its cost is higher than that of calcium hypo­chlorite. The reasons for this shift are listed by E. N. Poor (1) in his Nonfibrous Paw :iaterials Report for 1945 as follows: savings in chlorine, no sludge disposal problem, complete use of alkali, cleaner pulp, savin in space, and some advantages in the way the pulp handles on the wire. Some experimenting has been done in the use of chlorites in the bleaching of deinked stock, but, to date, this method has not found acceptance in the deinking industry. Fading Characteristics QI_ De inked Stock f e. �) Fading is defined by 'Webster's new International Dictionary [J(), as a gradual loss of intensity, color, distinctness, etc. In the paper industry this term is used synonymously with others such as color stability and light stability. TAPPI Routine Control ]flethod RC-50 is the usual means of measuring the degree of fading in the paper industry. This method employs the use of an Atlas Fade-Qneter for fading the sheet and a comparison of exposed and masked portions of the sample by any suitable method. 5 P. Nolan, J. A. Van den Akker, and W. A. Wink (2 ) state thatthere are at least two photochemical reactions in the discoloration of pulp. One is the so-called bleaching action produced by radiation of wavelengths longer than 385 mmu. The second is the normal dulling action caused by the action of light "!8-Velengths shorter than 3 6 mmu (ultraviolet light). Thus, some pulps �ill gain in brightness when exposed,to light while others will fade. This fact was proven in an experiment perfon:ned by J. H. Graff (3) in which he exposed different kinds of pulps to both sunlight and a sterilamp for 192 hours. The results showed that hardwood sulphite, kraft, and soda pulps gained in brightness while groundwood and softwood sulphite pulps decreased in brightness. H.F. lewis and D. Frornnuller 4), experimenting with groundwood pulp, found that there were apparent losses in the sulfuric acid soluble lignin fraction, the Cross and Bevan cellulose fraction, and the pentosans fraction of the pulp plus partial demethylation of the lignin when the sheets were exposed in a Fade-Qneter. Upon exposure of a 45 per cent groundwood -55 per cent� sulphite with 15 per cent clay sheet to sunlight for 73 hours per side, Lewis and Fronmuller fouhd the same losses except that the Cross and Bevan cellulose fraction did not change, although the Copper No. and the acidity of the sheet were increased. Nolan, Vanden Akker, and Wink (2) in experimenting with the fading characteristics of groundwood found a remarkable similarity in the spectral sensitivity curves of groundwood with the spectral absorption curve of lignin derivatives. Since the pulps with high lignin content (groundwood an u� s.w. ·sulphite) showed fading tendencies:; a marked chemical change was6 v.1uJV �hown in the lignin content of faded sheets; and there ;Ls-- a rei:na.rkable similarity in the spectral sensitivity curve of groundwood and the spectral absorption curve of lignin derivatives; it seems reasonable to assume that the major factor in the color stability of pulp is its lignin content. Deinked stock varies greatly in lignin content. Therefore, to obtain minimum fading characteristics in deinked stock, one should use no groundwood, unbieached softwood sulphite, or other highly lignified papers in his system. Three stage, and to a lesser extent_, two stage bleaching, remove the lignin fraction of the pulp; therefore, it seems reasonable that these bleachi systems should produce a bleached stock which is fairly light stable. Other factors, besides the groundwood or lignin content, which influence the color stability of bleached stock are as follows: · l. The final pH of the bleaching system dictates somewhat thefading characteristics of the bleached stock. F. Casciani and G. K. Starin (5) in experimenting with sulphite pulp found that a minimum of fading resulted when the final pH of the hypochlorite stage of a two-stage bleach was high (10 or above). In a single­stage bleach these men found that this effect was almost the reverse. The most stable color was obtained when the final pH was less than 5 • 75 • 2. Atmospheric conditions have an effect on the color stability ofbleached stock. P. Nolan, J. A. Vanden Akker, and W. A. Wink(2) state that all things being equal groundwood fades more rapidlyunder conditions of high temperatures and relative humidities. Ofcourse, these conditions must be accompanied by the action of lightin order to produce fading.7 3. An excess of iron in the washing water may also produce colorreversion 'as stated by E. L. Keller and F. A. Simmonds (6).4 •.. Aging will also cause paper to fade. This phenomena"'is probably due to oxidation taking place, and has been proven by H. F. Tauner and W. K. Wilson (7). Some attempts have been made to redu,ce the fading characteristics of a sheet by the addition of an inhibitor to the sheet. H. F. 'Tu.uner and W. K. Wilson (7) found that the light stability of newsprint was very materially increased by buffering the sheet at a pH of 7.2. The sample was dipped in a solution of N:l.HC03, and after drying was found to retain 0.12 €:1Il• of NaHC03 at a pH of 7 .2. A study by E. A. Reineck and H. F. Lewis (8) of 130 organic compounds as inhibitors to the fading of groundwood under the influence of ultra­violet light revealed no noticeable improvement in behavior. But P. A. Nolan (9) found that,the addition of Eastman Ultraviolet sensitizing solution reduced appreciably the fading of groundwood. The use of this compound is not feasible because of both high initial cost and cost of application. The results, however, support the premise that fading may be reduced or eliminated by the inclusion in a sheet of a compound which would strongly absorb the ultraviolet light which is responsible for fading. The use of fluorescent purple was found ineffective as a reducing agent for the fadin of groundwood because it does not brighten the ground wood sheet as it does bleached chemical pulps. Analyzing the material covered, ultraviolet light is responsible for the photochemical reactions which produce fading in bleached deinked stock. These reactions may be accelerated by heat and high relative 8 humidity. The main constituent of deinked stock which influences . its color stability would appear to be its groundwood content since this fraction is almost entirely responsible for the lignih content of deinked stock. Another factor which cannot be controlled is the aging of paper which causes it to slowly lose its brightness. By eliminating these factors or the inclusion of an inhibitor in the sheet, the paper produced should show good light stability properties. 9 Experimental Work S'ince the lignin content has an important influence on the fading characteristic of pulp, it was decided to bleach three different stocks of approximately 10, 20, and 30 per cent groundwood. Caustic deinked stock of about 10% ground­wood coneent, by microscopic analysis, was obtained from the Monarch Div., Allied Paper Mills, Kalamazoo, Michigam. The original furnish of this stock was as follows: 600 lbs. shavings, 2990 lbs. book, 3248 lbs. ledger, 5% caustic, 206°F, at 5� consistency. The deinked stock was divdded into three parts, and laboratory caustic deinked newsprint was added to two of the samples to bring their .groundwood content up to approximately 20 and 30 per cent. The three stocks w.ere then screened on a Valley Iron Works laboratory flat screen, 0.01 inch slots, and collected on a 60 mesh screen. Permanganate numbers were taken on each of the stocks, and the equivalent bleach consumption was determined by using the factors for sulphite pulp. The results are tab­ulated in Table I. Permanganate Number and Equivalent Bleach Consumption of Deinked Stock (TAPPI stand­ard T 214 m-50) Pulp lOo G.W. 20% G.W. 30% G.W. Permanganate 6.15 9.75 13.25 -Table I-Eq. Bleach 2.80 4.65 6.50 Twenty five grams of b.d. {bome dry) stock from.each of the three sample stocks as then bleached by jhe single, two, and three stage a9p�tlinlhJP-OChlorite bleaching methods. These10 stocks were bleached to approximately the same brightness by use of the equivalent bleach consumption figures obtained. The results showed a range of 5 units (Photovolt) between the nine bleached stocks. The identical b�ightnesses were desired so that the fading results could be comparable. The condit­ions for each bleach were as follo.ws: Single Stage Bleach Consistency------------------- 6 per cent Chlorine (from NaOCl)--------- 100% of eq. bleach 0 consumption Temperature------------------- 100 F Per cent completion----------- 98 per cent pH (phenylphthalein)---------- 8.5-9.5 Two Stage Bleach Chlorination stage: Consistency------------------- 3 per cent Chlorine �from Clawater)------ 60% of eq. bleach consumption Temperature------------------- 72 °F Per cent completion----------- 98 per cent Hypochlorite stage: The same as for single stage bleach except that the per cent chlorine (from NaOCl) was equal to 40% of the equivalent bleach consumption for the stock. Three Stage Bleach Chlorination stage: The same as for the chlorination stage of the two stage bleach except that the per cent chlorine (from Cl�water) was egual to 50% of the equivalent bleach consumption for the stock. 11 Alkaline extraction stage: Consistency------------------- 6 per cent Caustic soda (based on b.d. -- 2 per centpulp) Temperature------------------- 120°F Time-------------------------- 2 hours Hypochlorite stage: The same as foe single stage bleach except that the per cent chlorine (from NaOCl) was equal to 25% of the equivalent bleach consumption for the stock. Brightness waterleaf handsheets were then made of the bleached stocks following TAPPI standard T 218 m-48. The handsheets were then faded in an Atlas Fade-Ometer for periods of 1, 2½, 5, 10, 20, �o, 60 1 80, and 100 hours. At the end of these periods brightness readings were taken of the masked and unmasked portions on the Photovolt brightness meter and their differences calculated. All samples werefaded simultaneously. The temperature in the Fade-Ometer was held between 90-95°F and the humidity was held constant. The results obtained are illustrated in Fig. I. Certain trends which may be deduced from the gra�are as follows:1. The higher the number of stages of bleaching the lesswill be the fading of deinked stock.2. The groundwood content has more influence on the fad•lng of deinked stock than the number of stages ofbleaching.3. The higher stage bleaching has more effect on thefading of deinked stock in the higher groundwoodrange than in the lower groundwood range.12 •• The differ:rmce in fading between two consecutivestages becomes less as the number of stages increase.Thus, it follows that the groundwood content has the most effect upon the fading characteristics of deinked stock. The number of stages of bleaching will ffrect the fading char­acteristics of the stock to a smailer extent, but not enough to warrant its use as an economical control in the fading of bleached deinked stock. Therefore, inorder to reduce the fading of bleached deinked stock its groundwood content must first be reduced if possible. If impossible, an increase in the number of stages or bleaching will produce a small change. 1� Literature Cited 1. Poor, E. N., �- Assoc. Papers 29:491-497 (1946)2. Nolan, P., Vanden Akker, J. A., and \Vink, W. A., Tech. }:ssoc.Papers 28:162-1663. Graff, J. H., Tech. Assoc. Papers 25 :612-6164. 1.ewis, H. F. and Fronmuller, D., Tech. Asso.Q_. Papers 28:166-1695. 09.sciani, F., and Storin, G. K.,- Tech •. Assoc. Papers 26:li25·4336. Keller, E. L., and Simmonds, F. A., Tech. Assoc. Rtpers 26:434-440 (June, 1943)7. Tauner, H. F., and Wilson, W. K., Tech. Assoc. 1:§.pers 26:139-147• Reineck, E. A., and Lewis, H. F., Tech. Assoc. Fapers 28:169-1729. Nolan, P. A�, Tech, Ji.ssoc. Papers 28:173·177I/) (/) 12. l-!-Uc..:+.:-.:.;+i--;..µ;..!..;..:.j,.,-.-...;;.i...+,..;.h,'�._.;...,_,� ....... ��.;._µ..:..�...;...;.µ.:..,�.µ....1,-1,-,-'..i.+-.;.....!+'-..i...µ�j.......i-,-14��-+�h-1-......+-, ....... µ...-4-.,.... (l) t:: +:l ,, -C 0.0 ,.1 . /OJ.,.--+�'�!....i.-1---#-��-.... ,--�-;f--9 .p 0 8 i-:.;+1--#)�-..f.,.._,.;.+���.:.o--.-;-:;..r..:::,..i.:.::... > 0 25 JN 

The Influence of Single, Two, and Three Stage Bleaching on Fading Characteristic of Deinked Stock

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The Influence of Single, Two, and Three Stage Bleaching on Fading Characteristic of Deinked Stock

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