Deinking Chemistry FINAL

8/3/2019 Deinking Chemistry FINAL

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Deinking Chemistry

Tea Hannuksela, Kemira Germany GmbHScott Rosencrance, Kemira Chemicals Inc.

Content

Introduction................................................................................................................. 1Deinking chemistry ..................................................................................................... 2

Traditional deinking chemistry................................................................................. 2Neutral and low alkali deinking................................................................................ 3

Surfactants ................................................................................................................. 4Fatty acids............................................................................................................... 6Synthetic surfactants............................................................................................... 7

Blends..................................................................................................................... 8Other deinking aids................................................................................................. 8Emulsions ......................................................................................................... 8Modified Inorganic Particle (MIP) ........................................................................ 8Enzymes.............................................................................................................. 8

Factors to consider when choosing deinking chemistry.............................................. 9Recovered paper furnish......................................................................................... 9

Wood-free papers.............................................................................................. 10Deposits and catalase problems........................................................................... 11

Conclusions .............................................................................................................. 11References ............................................................................................................... 11


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IntroductionRecovered paper composition usually includes fibres, fillers, fine material and oftenink. When present the amount of ink is only around 2-5 wt% of the recovered paper.The primary goal in the recycling of recovered papers containing ink is to selectively

remove the ink relative to the solids present in the paper. Theoretically, if a paperonly contains 2-5wt% ink then the overall yield in deinking could be 95-98 wt%. Theyield is normally between 60-90% depending on the paper raw material and deinkingprocess used thus enabling a variety of specialty chemical and mechanical solutionsto favourably influence ink removal selectivity.

A wide variety of recovered papers are deinked. Each of these recovered papergrades has differences in both fibre and filler characteristics. For instance, oldnewspaper (ONP) is mainly composed of bleached mechanical pulp fibres orrecycled fibres while old magazine (OMG) usually also contain some bleached

chemical pulp. Mixed office paper (MOW) is almost exclusively bleached chemicalpulp.

Inorganic solid or ash in the recovered paper can range from about 10-40%depending on the paper grade. This ash can be present as either a filler or a coating.The most common fillers used in paper and coating is calcium carbonate and kaolin(clay).

Based on the combination of recovered paper being used and the desired final pulprequirements a variety of different deinking processes may be utilised. Flotationdeinking tends to be more selective than wash deinking and thus results in higher

yields. The selectivity in both flotation and wash deinking can be dramaticallyenhanced by utilising one or more specialty chemicals. It is well understood thatflotation and wash deinking are dominated by different physico-chemical propertiesand as such the two processes usually require different types of chemicals.

In wash deinking, the removal mechanism is largely based on the size of the particleto be removed. More specifically, the probability of a given particle successfullynavigating a mat at a given consistency and porosity increases as the size of thatparticle decreases assuming the ink particle does not become so small that it thencan destabilise and reattach in some manner to the fibre surfaces. Based on thismechanism wash deinking tends to be enhanced by addition of surfactants that

efficiently assist in detaching ink particles from the fibre substrate as well as thendispersing the detached ink particles. Therefore, hydrophilic surfactants (higher HLB)are generally used to assist with detergency and ink dispersion.

In flotation deinking, the released ink should also be detached from the fibresubstrate and dispersed in order to avoid redeposition. However, in flotation deinkingthe probability of removal of an ink containing particle is driven by a combination ofsize and surface energy. In flotation deinking a certain amount of agglomeration ispreferable as the removal in flotation deinking is dependent on the size of theparticle. The optimum size range is often stated to be between 50 and 150micrometers. Size alone however is not sufficient, additionally the agglomerates

should demonstrate surface energy properties that are more hydrophobic than washdeinking in order to allow for stable attachment and transport by air bubbles.


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The proper selection of deinking chemistry is often a compromise between costs andperformance. Some mills do not use deinking chemicals but on the other hand use amore expensive and higher quality recovered paper to reach a certain target. Othermills save costs with the recovered paper by using a lower quality furnish and thenuse deinking chemicals. One of the large production costs for a deinking mill come

from the recovered paper. The costs for pulping chemicals are often around 10-20 /tand bleaching may be the same or up to double the amount depending on bleachingdosages and sequences.

Recently due to increasing chemical, energy, and pulp prices mills are exploring newways of saving costs using new concepts for recycled fibre processing. Somechemical suppliers offer neutral deinking where chemical costs in the pulper can besaved in addition to other process and chemical benefits. Due to the complexity ofthe entire recycling process and the inter-dependency of each process step, it is notsufficient to only look at the pulper or flotation stage but rather the entire process.

Deinking chemistry

Traditional deinking chemistry

Deinking chemicals are generally added to the pulper (Lassus 2000). During pulpingthe recovered paper is slushed into a pulp at high consistency. The combination ofchemical and mechanical action is favourable. Additionally, by dosing early in theprocess to the pulper the reaction time is increased as well as the more effectivedosage of some chemicals as the result of a high consistency. Figure 1 shows aschematic layout of a typical deinking process for the production of pulp for graphical

grade paper. Often all deinking chemicals are added to the pulper, but sometimessome or all of the deinking aid can also be added to the flotation cell.

Figure 1. Schematic layout of a deinking process for the production of deinked pulpfor graphical grades showing possible addition places for deinking and bleachingchemicals.

Pulping Cleaning &Screening

1st

Flotationloop

Thickening

2st

Flotationloop

Thickening Bleaching

Dispersing/bleaching

Cleaning &Screening

Storagetank

Deinking chemicals- NaOH- Water-glass- H2O2- Soap/surfactant

Deinking chemicals- Soap/surfactant

(optional)

Bleaching chemicals- H2O2- Water-glass- NaOH- Chelant

(optional)

Deinking chemical- Soap/surfactant

(optional)

Bleaching chemicals- H2O2- Water-glass- NaOH- Chelantor- reductive bleaching (dithionite,

FAS or Borino)


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A variety of deinking aids exist. In traditional alkaline deinking these aids are oftencomposed of fatty acids and/or non-ionic surfactants. Sodium hydroxide (NaOH) isalso added for reasons such as ink detachment and ink dispersion. It is commonlybelieved that ink detachment is improved using sodium hydroxide both because offibre swelling effects as well as chemical hydrolysis of some bonds between the

substrate and some ink species. The pH at the exit of the pulper is often between8.5-10.5 when deinking a newspaper/magazine furnish.

In systems utilising a fatty acid containing deinking aid the level of water hardnesscan be important. Often a source of calcium such as calcium chloride is added to theprocess in order to ensure that the fatty acid soap is converted to its insolublecalcium-salt, which is believed to be the preferred speciation of fatty acid for inkcollection in flotation. Target levels of calcium are often on the order of 100-200 ppm.

The alkalinity present in traditional alkaline pulping can induce unwanted yellowing ofthe fibres. In order to offset such yellowing and associated brightness losses

hydrogen peroxide (H2O2) is often added to the pulper. In some systems one or morechelants are added to improve the peroxide bleaching efficiency by renderingdetrimental metal ions inactive with regard to unwanted peroxide decomposition.Finally, sodium silicate (or water-glass) is commonly used. The role of sodium silicateis complex and includes complexation of some detrimental metals and contribution topH buffering in some circumstances. Water-glass also helps in stabilising thereleased ink so that it does not redeposit on the fibre surfaces and contributes to inkparticle agglomeration and flotation efficiency. Finally, in many situations water-glasstends to depress the removal of filler during flotation.

The bleaching effect of hydrogen peroxide in the pulper is generally limited and theconditions are usually not optimal for such bleaching. As a result it is normal to post-bleach the pulp following deinking. This bleaching can involve either hydrogenperoxide bleaching (oxidative) and/or hydrosulphite bleaching (reductive). Typicalreductive bleaching agents also can include formamidine sulphuric acid (FAS) andBorino (alkaline sodium borohydride + sodium bisulphite) (Vahlroos et al. 2008).Reductive bleaching is performed at a neutral pH. Figure 1 also shows some typicalpositions where bleaching can be performed such as pulper, disperger or postbleaching.

Neutral and low alkali deinkingA new trend for certain processes and mills in the deinking of newspaper andmagazine based raw materials is to move away from traditional alkaline deinking andtowards lower pH levels which are commonly referred to as true neutral deinking(pH about 6.8-7.2) and reduced or low alkali deinking (pH about 7.2-8.8). Oftenthese desires are driven by chemical cost savings and/or environmental factors.

In true neutral deinking only surfactant, usually a blend of different syntheticsurfactants, is added to the pulper (Rosencrance et al. 2005). In reduced/low alkalinedeinking sodium silicate is also added in addition to the surfactant. Another, usuallyless successful approach, has been adding sodium sulphite to the pulper along with

a deinking aid (Lapierre et al. 2004). Chemical cost savings in at least NaOH andhydrogen peroxide and sometimes water-glass and/or chelant are achieved.


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Often in all forms of neutral deinking the brightness of the pulp will be lowercompared to alkaline deinking due to the removal of hydrogen peroxide from thepulper although ink removal can be very similar once the chemistry is optimised.

As described above, pulper bleaching is not optimal for optimum utilisation of

hydrogen peroxide (low consistency and temperature as well as competingcontaminants). It has, in fact, been shown that this brightness gap obtained usingvarious neutral deinking approaches can be regained if the process contains adisperger or post-bleaching stage with hydrogen peroxide (Vahlroos et al. 2007). Thismeans that additional chemical cost savings can be achieved. Other benefits oflowering pH can include improved stickies removal (see below), lower release ofsubstances into the process water, and lower water treatment costs in areas such aswater clarification. Neutral or low-alkali deinking may not work on all paper rawmaterial grades or in all processes and requires strong technical knowledge whenconverting from traditional alkaline to neutral deinking. Drawbacks of neutral deinkingif not optimised may be insufficient ink release, ink fragmentation and lower yield.

Mills producing pulp from mixed office waste (MOW) containing mainly chemical pulpfibres often already operate at neutral conditions. These mills often use less deinkingaids and can run without surfactant in some cases. With such a raw material, inkremoval is not a problem, but rather the presence of larger dirt specks from variousprinting inks. These specks are usually handled mechanically in a disperging stageand in some situations can be handled using certain specialty chemical additions.

Surfactants

Surfactants are surface active agents. This chemically unique species have a dualcharacter. This character consists of hydrophilic and hydrophobic portions of thechemical structure. In an aqueous environment, the hydrophilic portion is water lovingand relatively polar while the hydrophobic part of the surfactant is water hating andrelatively non-polar (Figure 2). Surfactants can be non-ionic, anionic, or cationic. Forthe anionic and cationic species the hydrophobic part normally includes ahydrocarbon chain (-CH2-CH2-) and the hydrophilic part includes a variety ofchemical functionalities. These can include entities such as an amine group (-NH3),a carboxyl (-COOH), sulphonate (-SO3), or sulphate (-SO4) group among others.Non-ionic synthetic surfactants generally contain blocks or units of variousalkoxylates, most commonly derived from either ethylene or propylene oxides.

Figure 2. Schematic picture of surfactants.

Hydrophilic head- carboxyl group- sulphate- other polar end

Hydrophobicblock/unit

Hydrophilicblock/unit

Hydrophobic tail- hydrocarbon chain- non-polar chain


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As a result of these unique chemical compositions and the associatedthermodynamics when placed in solutions containing surfaces and interfacessurfactants tend to demonstrate unique properties as a result of attempting tominimize the free energy associated with their presence in a given environment. To

this end, surfactants modify surfaces and/or interfaces between various phases thuslowering the interfacial energy. This modification of the energetics at surfaces andinterfaces allows a number of phenomenon to occur. One such example, isdetergency and removal of contaminants from solid surfaces such as printed ink on afibre surface in paper recycling.

One common framework suggested is that this detergency assists a hydrophobic inkconstituent to energetically depart from a preferred solid fibre surface and disperse ina hydrophilic and uncomfortable aqueous environment (Figure 3). The surfactantmediates this energetically unfavourable process by altering the surface andinterfacial energy thus facilitating ink detachment and dispersion in the water phase

thus making possible subsequent separation from the desired fibres dispersed aswell in the medium.

Figure 3. Release of ink from surface with the help of surfactants.

Ink on surface (paper fibre) inwater.

Surfactants accumulate atinterfaces, lower the interfacialenergy facilitating release of theink.

The ink is released and stabilisedinto the water phase


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Because the presence of surfactants in an aqueous environment assist to lower thesurface tension of the liquid (water) it becomes possible to produce and maintain afoam.

Surfactants have solubilities in the medium in which they are distributed. Typically, if

surfactants are sufficiently soluble a concentration can be reached referred to as thecritical micelle concentration or CMC. The kraft point is the temperature at which thesolubility of a given surfactant equals the CMC of that surfactant. Once the CMC isachieved a series of new physical chemical phenomena occur and as such lead to avariety of unique and valuable attributes. The effect of the CMC is rooted inminimisation of the surfactants free energy in a given system. The CMC depends onthe temperature and composition of the aqueous system and is unique for eachsurfactant and system. Concepts such as micro-solubilisation are directly linked tomicelle formation.

Fatty acidsFatty acids have been used to produce fatty acid salts (soaps) for centuries. Thesesoaps have been used to remove dirt from different surfaces. Fatty acids consist of along hydrocarbon chain (-CH2-CH2-) with a carboxyl group, typically at the terminusof the molecule. The hydrocarbon chain can be saturated or unsaturated (containingdouble bonds) depending on the origin of the fatty acid. Saturated fatty acids, suchas stearic acid (18 carbons) or palmitic acid (16 carbons) are solid at roomtemperature while unsaturated fatty acids, like linoleic acid (18 carbons with twodouble bonds at the 9 and 12 positions) can be liquid (see Table 1). Fatty acidproducts are normally mixtures of several fatty acids with different structures.

Vegetable based fatty acids normally consist in large part of mixtures of unsaturatedfatty acids (oleic, linoleic and linolenic acid) while animal based (tallow) fatty acidsgenerally consist in large part of mixtures of various saturated (stearic, palmitic acid)and unsaturated fatty acids (oleic acids).

Table 1. The structure of some fatty acids normally found in deinking aids.Fatty acid Structure Short

nameMeltingpoint

Palmitic acid CH3(CH2)14CO2H C16:0 63 CStearic acid CH3(CH2)16CO2H C18:0 69 CPalmitoleic acid CH3(CH2)5CH=CH(CH2)7CO2H C16:1 0 C

Oleic acid CH3(CH2)7CH=CH(CH2)7CO2H C18:1 13 CLinoleic acid CH3(CH2)4CH=CHCH2CH=CH(CH2)7CO2H C18:2 -5 CLinolenic acid CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7CO2H C18:3 -11 C

Fatty acids, being anionic salts of carboxylic acids, demonstrate different propertiesdepending on pH and the presence of various other ionic species present in thesolution. In acid form, the fatty acids are nearly insoluble in water but upon addition ofalkalinity to elevate the pH the fatty acid transitions to form an essentially water-soluble fatty acid soap. If calcium ions are present the fatty acid soaps form relativelywater-insoluble calcium fatty acids soaps. A number of metal-fatty acid complexesand speciations can exist depending on the overall composition of the system. The

calcium soaps are good ink collectors in flotation deinking processes. These benefitsare the result of the calcium soaps simultaneously impacting both the surface energyand size of ink containing agglomerates.


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Fatty acid soaps are often formed by pre-neutralisation of the fatty acid in thepresence of alkalinity prior to introduction into the repulping system. It is important toalso evaluate the entire pulping and papermaking process to ensure that nounfavourable metal soaps, such as calcium fatty acid soap, are contributing to

deposit problems. Fatty acid dosages to the pulper normally range between 3-7 kg/tor 2-4 kg/t to the flotation cell.

In processes where high amounts of newspaper are used, like in the US, mills tend touse more synthetic surfactants or blends rather than pure fatty acids. This is in partbecause the synthetic surfactants allow for more controlled and enhancedmodification of surface properties especially in the areas of ink detachment and inkdispersion.

Synthetic surfactants

Normally non-ionic synthetic surfactants are used directly or often can be part of amulti-component deinking aids or blend. The most common synthetic surfactants indeinking are ethoxylated (EO) and/or propoxylated (PO) fatty acids or fatty alcohols.These are non-ionic surfactants. Figure 4 shows the structure of some alkoxylatedsurfactants. The number and distribution (block or random) of EO and PO unitsdetermines the properties of the surfactant.

a) b)

c)

Figure 4 a) Ethoxylated fatty acid, b) propoxylated fatty alcohol and c) EO-PO blockpolymer.

The choice of synthetic surfactant as a deinking aid depends on several things.Simplistically, the surfactants are chosen based on both their HLB value and theprocess temperature as well as the type of recovered paper being recycled. Thesefactors are primary in determining the surfactant properties and application range.Above a certain temperature, the so called cloud point, the surfactant forms asurfactant rich phase which is non-homogeneously distributed in the system thushindering performance. The cloud point is a collective function of the entire aqueouschemistry and the non-homogeneous phase is fully reversible if the temperature isdecreased.

Synthetic surfactants when properly selected demonstrate very favourable ink

detachment and ink dispersion characteristics. There is not one optimal surfactantthat will work equally well in all processes and conditions, but rather each process, ormore precisely even every process step, requires different functions from the


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surfactants. Therefore, tailor-made blends of fatty acids and synthetic surfactants areoften the best option (see next section).

Generally, synthetic surfactants themselves are more costly than fatty acids.However, the required dosages are also significantly lower. Dosing of synthetic

surfactants is generally easy as they are liquid at room temperature and thereforeonly need a pump for dosing.

Blends

As mentioned above, there is not one universal surfactant that would performoptimally in all processes and under all conditions. Each process step requiresdifferent physico-chemical conditions. In the pulper, ink detachment and inkdispersion is crucial. In flotation again ink hydrophobisation, aggregation andcollection is important as well as good foam properties. Deinking chemicals shouldoptimally contain chemicals for each of these micro-processes. Fatty acid-syntheticsurfactant blends can combine the best properties of both systems into one chemicalblend. The dosage of blends depends naturally on their chemical composition but isnormally somewhere between 1-3 kg/t. Alternatively, the dosage can also be splitwith one blend optimised for the pulper and another for the flotation cell. Liquidblends are most common.

Other deinking aids

Emulsions

Due to the difficulty in handling some fatty acids which can be solids/semi-solid atcommon atmospheric temperatures of interest formation of liquid emulsions and/ordispersions are often made. In many cases the fatty acid is saponified and in allcases the products contain at least one emulsifying/dispersing agent. These agentsare commonly non-ionic surfactants. Fatty acid levels in these products can rangefrom 10-50 wt%. Emulsions/dispersions may be used in smaller deinking mills thatdo not have a saponification unit.

Modified Inorganic Particle (MIP)

In order to improve the collection in flotation deinking systems a new technology hasbeen developed (Rosencrance et al. 2007). This is based on introducing a

hydrophobically modified inorganic particle (MIP) to the pulper. The particle willcollect hydrophobic substances like ink and not only improve flotation deinkingselectivity but also significantly reduce ink re-deposition. This technology is new andhas shown very promising results in mill scale trials where very low attached inkvalues have been observed.

Enzymes

In some mills an enzyme containing additive is introduced. The concept is based onthe possibility that some enzymes can efficiently facilitate favourable chemicalreactions. For instance, these species can assist in ink detachment from fibre

surfaces. Some propose that cellulases and hemicellulases can alter the fibre surfaceand thus contribute to release of ink. Lipases are proposed to attack fatty acids and


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resinous substances from wood and any fatty acid or oil related carriers in the inkwhile laccase is offered to assist in modifying the lignin on the fibres.

Enzymes generally are sensitive to both temperature and pH thus limiting theefficiency in some commercial cases. Additionally enzymes are quite expensive to

produce although often the added dose can be small. Certainly, the use of enzymesis an environmentally good option. Additionally strength improvements as well asfaster drainage of the fibres have been proposed in some situations after enzymatictreatments. At present, mainly mixed office waste mills are using these productswhich prefer neutral conditions with a primary goal of reducing dirt specks.

Factors to consider when choosing deinking chemistryAs discussed above, selection of the appropriate deinking aid is based on a multitudeof factors. Below are some factors worth considering for the production of deinked

pulp destined for the manufacturing of graphically printed paper or tissue. Recyclingof board normally does not involve deinking.

Recovered paper furnish

The base paper quality and the printing method are well known to be directly relatedto deinkability. Two of the most common printing methods are offset and rotogravureprinting. Utilisation of water-based flexographic printing is getting more common insome geographic regions. These are conventional or mechanical printing methods.Additionally, digital or electronic printing is of increasing utilisation. Methods such aselectrophotograpy (xerographic or laser printers) and ink-jet printing are examples.

The components in the printing inks vary among printing methods as does theapplied ink layer thickness. Different base paper qualities are therefore preferred forsome printing methods. The choice of printing method is also dependent on the finalprinting quality demand, the cost requirements of printing, as well as number and rateof copies produced.

Different recovered paper furnishes demonstrate different issues. For instance, offsetinks are known to become more difficult to deink with the combination of time and/ortemperature or age. Alternatively, if the furnish contains high levels offlexographically (water-soluble ink) or ink-jet (small colour pigments) printed papersincreased amounts of process washing and/or lower pH is often beneficial.

Table 2, as reproduced from previous work by Eklund and Lindstrm, shows thecomposition of the base paper, coating and printing method used for different papergrades as well as the most common deinking method and the use as end product.The values in the table are generalisations and exceptions can exist. Magazine paperis today also produced with increasing amounts of deinked pulp which is notindicated in the table which originated in 1991.

The base paper can be either uncoated, supercalandered (SC, smoothened underhigh pressure) or coated. Newspaper is generally uncoated while magazine papersare often either supercalandered or coated.

A high content of newspaper in the furnish leads to a need for chemistry to assist inink detachment, especially if the newspapers are old or have experienced hot


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summer weather. Generally, blends or synthetic surfactants work well on suchfurnishes. Due to increasing prices and scarcity of raw material in certain regions,lower quality raw material is often used. The quality is not only lower, but the qualitymay vary significantly which requires more flexibility from the deinking aid.

Table 2. General information about newspaper, magazine and fine paper (modifiedfrom Eklund and Lindstrm 1991).

Raw material Fibre type Fillercontent (%)*

Printingmethod

Deinkingmethod

DIP end-use

Newspaper 100% MP orRCF

0-15RCF Offset, flexo Flotation News

Magazine-SC 50% MP,

25%BKP (SW)0-40CC,k Offset, roto Flotation News

-LWC 50% MP,50%BKP (SW)

20-45CC, k, Ti Offset, roto Flotation News,Magazine

Fine paper 85% BKP(HW&SW)

12-45CC, k, Ti Offset, electro,ink-jet

Flotation,washing

Tissue

*Total filler amount, i.e. base paper + coating filler content (% of final paper)SC= supercalandered, LWC= light-weight coatedRCF= recycled fibre, MP=mechanical pulp, BKP=bleached kraft pulp (chemical pulp), UBKP= unbleached kraftpulp, SW=softwood, HW=hardwood,RCF

= filler from RCF up to 12%,k= kaolin,

CC=calcium carbonate,

Ti=TiO2

Coatings in magazines can contain appreciable levels of dispersing agent which wereused in the coating process to assist in dispersing the fillers in the coating. Thesedispersants are at times surface active and together with alkali can lead toacceptable ink detachment from the coated magazine paper. At the same time theseadditives can hydrophilise ink containing agglomerates and hinder flotation efficiencyas well as contribute to unwanted foam generation and/or stability.

Wood-free papers

Chemical pulp based paper, such as office waste paper, does not demonstrate thealkaline yellowing and is normally not so much affected by pulping pH. The mainreason is that chemical pulp fibres are not sensitive to alkali-induced yellowing.Chemical pulp fibres have already been treated with alkali in the pulping processwhich is why these fibres will not swell to the same extent any more as mechanicalpulp fibres, i.e. ink will not be released more through fibre swelling which is why

neutral deinking conditions are more favourable for office waste paper deinking.Reductive bleaching is furthermore normally more beneficial for office waste papercompared to peroxide bleaching as the fibre brightness is high (chemical pulp) butcolour removal is necessary.

Laser printed papers or photocopied papers are, however, difficult to deink as thetoner has been melted, fused and bonded to the fibre surface. The toner is generallydetached as large flat flakes which are too large to be removed by flotation orwashing. The flakes become visible dirt specks in the paper if not removed ordestroyed. The flakes are in fact usually destroyed in disperger or kneader units inthe process. It is difficult to improve the deinkiability of office paper by chemical

means. Sometimes enzymes are applied.


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Deposits and catalase problems

Stickies result from additives present in the recycled paper such as glues andadhesives. These stickies if not passivated (tackiness reduced) or removed can leadto runnanility issues and inefficiency on the papermachine. Neutral-deinking or low-alkaline deinking is one option for such mills. Lowering the pH in the pulper will help

in maintaining the stickies particles large (Sarja et al. 2006). These less fragmentedstickies are then easier to remove by screens. Chemicals for stickies passivation orfixation also exist, but the preferred option is to remove the stickies from the processin a selective manner such as flotation and screening.

Catalase is an enzyme that is produced by micro-organisms (bacteria) as a defencemechanism. Catalase will decompose hydrogen peroxide used as a bleaching agentthus leading to increased cost and/or reduced brightness. Catalase is normallycontrolled by use of biocides. Removal of hydrogen peroxide from the pulper inneutral or low alkali deinking can reduce the catalase problems in the deinking mill.

ConclusionsThe demand for recycled fibre is globally increasing by more than 4% annuallycompared to around 2% for virgin fibres. This means that more paper needs to berecovered and recycled. As most countries in Europe already collect up to 63% (in2006) of all consumed paper, this means that the raw material quality will decrease inthese regions as also lower quality paper has to be recycled. At the same time higherquality of the final deinked pulp is demanded. A higher proportion of deinked fibre willalso be used in especially magazine grade papers. Newsprint is already producedwith 100% deinked pulp.

Another trend is the lower use of fresh water or higher closure of water circuits in themills which will also affect the deinking process (higher temperatures, more dissolvedand colloidal substances in the process waters, etc.).

All these trends signify that more deinking, bleaching and other recycling processchemicals are required to reach the same quality target. This will as a result requiremore work in order to find new chemicals and concepts that will help recycling mills tosave raw material, chemical or energy costs.

ReferencesEklund, D. and Lindstrm, T. (1991) In: Paper chemistry, Eklund, D. and Lindstrm,T. (Eds), Grankulla, Finland, DT Paper Science.

Lapierre, L., Bouchard, J., Dorris, G., Pembroke, C., Allen, J. and Hill, G. (2004) Milltrials on near-neutral sulphite deinking. Part I, Pulp&Paper Canada, 105:2, 42-46.

Lassus, A. (2000) Deinking chemistry. In: Papermaking Science and Technology,Book 7: Recycled Fiber and Deinking. Gttsching, L. and Pakarinen, H. (Eds.)Jyvskyl, Finland, Fapet Oy.

Rosencrance, S., Ngome, C., Hale, K. (2007) Use of modified inorganic particles indeinking US patent application US 2007/0158039.


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Rosencrance, S., Horacek, B., Hale, K. (2005) A unique new ONP/OMG true-neutral deinking technology, EXFOR Secondary Fibre Conference, Montreal,Canada.

Sarja, T. and MacNeil, D. (2006) Effect of neutral deinking on stickies, PTS-CTPDeinking Symposium, Munich, Germany, 15-1 15-13.

Vahlroos, S., Krkk, M., Rosencrance, S. and Niinimki, J. (2007) Comparison ofDIP bleachability between traditional soap and reduced alkaline chemistries,Proceedings from 8th Research Forum on Recycling, Niagara Falls, Ontario, Canada,292-301.

Vahlroos-Pirneskoski, S., Knutzen, R. and Niinimki, J. (2008) Basics of CombinedSodium Borohydride and Sodium Bisulfite Bleaching, Tappi J. (submitted).

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Deinking Chemistry FINAL