Deinking Technology; its Modification and Recent Developments: A Review

 

S.N.Panda¹,S.K.Biswal¹*, U.P.Tripathy²

¹Centurion University of Technology and Management, Ramachandrapur, Jatani, Khurda,

Bhubaneswar, Odisha-752050

²Pulp and Paper Research Institute, Jaykaypur, Rayagada, Odisha-765017

*CorrespondingAuthorE-mail:dr_skbiswal@rediffmail.com

Deinking is an important step for recycling of old waste writing, printing and newsprint papers. The demand of paper has been continuously faster than the availability of fibre from natural source. The efficiency of ink separation in the process of waste paper recycling depends on the ink properties, kind of the substrates, age of waste papers, the printing techniques and printing conditions. In general deinking process a large amount of chemical is required which makes this method expensive, pollution intensive and also not obtained a perfect quality. In the present paper a brief Journal review has been carried out on the recent developments in the deinking process and what are the better steps to obtain a standard recycle quality paper. Recycling of waste paper has been found to be more economical and eco-friendly.

 

 

 

INTRODUCTION:

Writing is a fundamental need of educational institutes. Fountain and ball point pens are used to improve the hand writing of children. Thus in every academic year papers stained with fountain and ball ended pen inks are being thrown out, so recycling of these papers is very much essential. The deinking process is the best technology for solid waste management. With this technology solid waste generation can be minimised as well as deforestation must be eliminated and protect the environment. The deinking plant must deals with a wide variety of paper types, ink types and printing techniques^1-5. From the mixture of recovered papers, the deinking papers, deinking plant is expected to produce a pulp of high quality. The main aim of this review work is to study the recent development of deinking process and the reutilization of newsprint, laser printer, coated and notebook papers by using several surfactants and additives.

 

Antonio et.al.⁶ (1996) reported the evaluation of flotation and washing process in deinking of old newsprint and office waste. According to them interchange the sequence of washing and flotation with low surfactant dosage achieved the highest overall performance. For high level ash stock, the washing-flotation sequence with 0.01% surfactant dosage achieved the maximum cleaning quotient. Pala et.al.⁷ (2006) studied the factors influencing MOW (mixed office waste) deinking.  According to them pre-washing the pulp facilitates the deinking process. Cellulolytic enzymes and deinking chemicals are comparable in terms of ink removal ability. The biotechnological approach in deinking of old news print is reported by Dhermander Kumar et.al.⁸ (2015), for this they used Trichoderma longibrachiatum at temperature 50-60°C at pH 5.5. Several experiments will carry out to increase the brightness and yield by maintaining the strength properties with low cost for formation of this deinking paper. Deinking is the removal of ink and other non fibrous materials from slurry of waste paper. According to Pauck et.al.⁹(2015) the effect of printing inks and adhesive  on the  recycling of  paper  is  composition of printing  ink vehicle 10 to 70 % colorant  5 to 30 % fillers and additives 0 to 10 % .Waters et.al.¹⁰(2015)explained maintaining  optimum consistency in the bleached stage is important to facilitates optimum brightness gains and also to minimise channelling, high bleach demand and high residual that are experienced if the consistency is too low. Cesar Basilio et.al.¹¹ (2015) used a deinking reagent, called DEKA-2000, is composed of the modified Kaolin and a surfactant specifically formulated to maximise the effect of this modified kaolin in flotation deinking. Carre et.al.¹²(2015) put forth the deinking process yield varies according to raw material and process. After washing significant loss is usually observed during dispersed flotation. To overcome the problem the innovative idea of process water and especially the role of released surface active substances on the flotation selectively. Pernget.al.¹³ (2015) suggested the effect of hot dispersion on the properties of deinking pulp as consistency of pulp is greater than 32%, the temperature effects were more significant than the consistency effects. The hot dispersion should be operated at temperature of 100 to 110°C and consistency greater than 32%.Hirch et.al.¹⁴ (2014) explained each proportion of 4% corrugated board in a basic mixture of recovered paper results in a one point loss in luminosity of the deinked pulp. A proportion of 30% inkjet printer    newsprint results in a luminosity drop of almost 7 points, combined with a shift of the colour locus into the green area. Fernadezet.et.al.¹⁵(2014) reported deinking of flexo-graphically printed paper by using cupric chloride. According to him Cu(II) ion reducing both the electrostatic and steric components of dispersed flexo-ink particles. Ricardet.al.¹⁶(2014) added soap contact time with recycled pulp improves flotation deinking efficiency and reduce cost. According to him optimisation of the fatty acid soap addition points increased soap contact time 9 to 20 minutes with recycled pulp before flotation. This in turn resulted in improved ink removal efficiency for three of four types of commercial flotation cells. Pathak et.al.¹⁷(2014) reported on enzymatic deinking of photo copier waste paper using crude cellulose and rylanase of Coprinopsis cinerea. They explained the application of crude cellulose and xylanase produced by fungas Coprinopsis cinerea in 100%photocopied papers the enzymatic deinking was found to be better than chemical deinking resulting in higher deinking efficiency, brightness and physical properties.

TYPES OF PRINTING INKS:

The inks contained in the recovered paper naturally also have a considerable influence on the deinking results. Inks are generally divided into two categories according to their floatability. These are mainly water-based and oil-based. Water based-inks have a hydrophilic surface and therefore cannot attach to the air bubbles and unable removed by flotation again. Oil based inks can be effectively removed by flotation, as they have a hydrophobic surface which allows them to become attached to the air bubbles. Other printing inks are given bellow.

 

1. News print ink:

News print inks, except were gravure printing is employed, dry by absorption of ink into the paper stock. The paper used is uncoated and posses a rough surface which allows the ink to penetrate rapidly. The ink contains mineral oil, pigment and little or no binder.

 

2. Latter press an offset ink:

Typographic and lithographic inks that dry by oxidation, by evaporation at elevated temperature, by penetration, by coagulation or by combination of these systems.

 

3. Flexographic ink:

Often called aniline inks are transparent inks consisting of a dye stuff dissolved in alcohol. These inks dry by evaporation of solvent.

 

4. Rotogravure ink:

These are combination of pigment, solvent and binder. The binders are resins, nitrocellulose, and ethyl cellulose and vinyl resins. About 35% of the rotogravure inks now sold have these gilsonite base, another 30% are made from rosin derivatives .These binders are strongly alkali resistant.

 

5. Special ink:

There are a large number of special types of inks. These include heat set, moisture set, steam set, quick setting, high gloss metallic, wax set, water colour, cold set. These inks are often used in the printing of breed wrappers, milk containers, frozen food containers, paper cups etc. Since the binders usually have a high acid number, they are unlikely to be troublesome in deinking¹⁸.

FLOW DIAGRAM OF RECYCLING WASTE PAPER MAKING:

 

Fig.1: Flow diagram of recycling waste paper

Sorting and grading is for the removal of unwanted materials and improving the quality of product by minimum energy and chemical consumption. Singer A¹⁹ (2014) explained recycled fibre more contaminated,but potentially more value represented in table-2. Rosker M²⁰ (2014) explained production of high quality paper grades utilising deinked pulp. Magazine papers are mostly coated with the ink smoothly printed onto the coated with offset or gravure presses (soft ink). Office papers are uncoated or only lightly coated and the laser print is virtually fused onto the paper surface (hard inks) which is given in table-1.

 

Table 1: Composition of typical rejects in waste paper recycling²⁰

 

Table 2: Composite of furnish and properties¹⁹

 

DEINKING PROCESS:

In the deinking process the main aim is to remove the hydrophobic contaminants from the recycled paper. The contaminants are mainly printing ink and stickies. Several processes are used but the most common is the flotation process.

1. Flotation Process:

Froth flotation is the most common and important process used in deinking paper industries. In this process the temperature is mentioned between 40-70°C with pulp consistency of 0.8-1.5% and pH should be about 7-9.Air is blown into the pulp suspension. The collector has affinity both to the ink particles and air bubbles, causing them to attach. The air bubbles lift the ink to the surface and form a thick froth that can be removed as given in figure-2. The particles are either hydrophobic from the start or made hydrophobic by adding suitable chemicals (surfactants). Sometimes the particle size is charged by using flocculants. Normally the setup is a two stage system with 3, 4 or 5 flotation cells in series. Flotation deinking is very effective in removing ink particles larger than about 10µm²¹.

 

Fig.2: Diagram of a froth flotation cell²¹

 

2. Wash deinking process:

Wash deinking consists of a washing stage where dispersants are added to wash out the printing inks. When the pulp slurry is dewatered, the medium to fine particles are washed out. This process is most useful for removing particles smaller then 30µm, like water-based inks, fillers, coating particles, fines and micro sticks.

3. Combined washing and flotation:

High quality deinking of office wastes and other printing papers often commonly uses a combination of washing and flotation.

 

 

 

4. Enzymatic deinking:

This method of deinking uses industrial and/or food grade enzymes in conjunction with flotation deinking to aid in the removal of inks in recycling mills. This process is more efficient in ink removing and increases fibre yield, decreases dirt count, and increases pulp brightness. Krishanamachary et.al.²² (2015) explained how the bio-surfactant along with enzyme is used by eliminating 100% chemical surfactants and 50% reduction of hydrogen peroxide and sodium silicate, for deinking process in laboratory scale. The result showed that bio-surfactants act as dual character of bleaching and as surface active agent which is given in table-3.

 

Table 3: Deinking performance results of bio surfactants and enzymes a comparison²²

 

5. Other Deinking Processes:

Dissolved air flotation (DAF) is used by some deinking paper mills in the deinking stage and can remove ink particles as well as filler particles present in paper.

 

CHEMICALS AND THEIR FUNCTION IN DEINKING & BLEACHING:

Printing inks are usually removed by flotation however; the inks must be separated from the fibers before flotation. Ink detachment from fibres occurs in pulping. The energy introduced into the paper or drum helps to disintegrate the fibre stock. The pulping equipment generates friction which helps detachment of ink particles. Dosing of deinking chemicals promotes the detachment of ink from the fibres. The main chemicals used for detachment of ink particles are caustic Soda (NaOH), Silicates and Hydrogen Peroxide (H₂O₂).

 

1.Function of NaOH:

In pulping function of NaOH reacts with fibre, water can penetrate more easily into the fibre network, while promoting fibre swelling. The fibre swelling loosens the fibre network, so the ink is completely detached in pulping. NaOH has two more works; it is an activator for H₂O₂and as a saponification agent in soap preparation.

 

2.Function of Silicates:

Na₂SiO₃ is a multifunctional standard  chemical in flotation deinking. It is a stabilizing agent for H₂O₂ and act as a pH buffer. Dennis et al²³(2014) explained the correlation of  pH value in flotation and ink elimination efficiency is written in table 3.

Table 3: Ink Elimination in % at Different pH²³

 

3. Function of H₂O₂:

The wood containing RP (recovered paper) and alkaline condition can induce  yellowing, which lowers the final DIP quality and H₂O₂ In pulping is to prevent yellowing.

 

4. Function of complexing agent:

Use of silicate or organic complexing agent such as Na₅DTPA (Pentasodium diethylene triamine pentaacetate) or EDTA(ethylene diamine tetra acetatic acid)are used in combination with silicate and avoid undesirable decomposition through detached heavy metal ions.

 

WASHING:

The goal of pulp washing is to eliminate disturbing particles smaller than 30µm. These particles are in particular fillers, coatings, fines, micro stickies, and printing inks^24-25.

 

FLOTATION:

1.      Function of collector:

Collectors like oleic acids and calcium salt of fatty acids are used to collect ink particles during flotation. Soap has to sufficient time to react.

 

2.      Water hardness:

If the water hardness is too low the sodium soap will not convert completely into calcium soap, if the water hardness is too high, the formed calcium soap particles are too large and the detached inks will not be optimally coated. The best water hardness and ensure the collector effect is 10 – 30°dh. If the hardness of process water is lies below 10°dh additional CaCl₂ has to be dosed.  Oleic acid are more expensive, hence the dosing of fatty acids equal quantitative to oleic acid.

 

3.      Silicon derivatives:

Silicon derivatives are a new group of collectors used as a direct alternative to fatty acids and soaps. Silicon derivatives have both hydrophobic and hydrophilic molecular components; they coat and collect the detached ink, fix it onto air bubbles and thus ensure optimal ink removal. But silicon derivatives cause a high loss of ash as compared to soap and fatty acids.

 

BLEACHING:

Recycled fibre pulp intends for the production of packing papers and board, are not necessary to bleach. For printing it needs bleaching to improve brightness and luminance. Bleaching agents are categorised into two types.

1.      Chlorine free compounds eg. H₂O₂, O₂, O₃, sodium thionite.

2.      Chlorinating agents eg. ClO₂, Cl₂, NaOCl

 

1. Function of H₂O₂:

The H₂O₂ bleaching can only be activated in the presence of NaOH. This effect is achieved by shifting the balance of H₂O₂/per hydroxyl anion in the alkaline medium to the right hand side.

H₂O₂ + OH^- H₂O + HOO^-

If the alkaline concentration is too high though it leads to the undesired decomposition of H₂O₂in H₂O and O₂

H₂O₂ + HOO^-→ H₂O + O₂ + OH^-

 

ADVANTAGE OF DEINKING PULP:

·        Freedom from complete dependence on market pulp.

·        Reliable source of pulp during times of market pulp shortage.

·        Price usually favorable compared to corresponding grades of market pulp.

·        The kind of deinking pulp suitable for use in printing papers usually impart special properties to the finished papers compared to similar papers made from wood pulp.

a.      Increased opacity.

b.      Less curling tendency due to changes in moisture content.

c.      Less fuzziness.

d.      Better formation.

e.      Better retention of size and fillers.

f.       Softer and less tinny character.

 

DISADVANTAGES OF DEINKING PULP:

·        Strength may be low, because the fiber may be shorter than is desirable for given paper.

·        Brightness may be low, which will restrict the production of deinked pulp which can be used.

·        The stock may be slow, resulting in poor drainage and limited paper machine speeds, addition of virgin pulp may be necessary to improve drainage on the wire.

·        There is often problem due to dirt specks in the paper caused by ink or other non fibrous waste paper constituents.

·        There may be serious trouble on printing press from sticky particles caused by adhesive materials,

·        There may be variation in color , brightness, strength and freeness of the deinked pulp from time to time, because of changes in the nature of waste paper furnish and of operating problem in deinking plant.

·        Variation in fiber composition may be troublesome.

·        The disposal of waste water from the deinking plant often presents a serious problem whose solution may be difficult and expensive.

·        The disposal of solids from the waste water, and of the trash which is removed from the deinked pulp may present a problem

 

CONCLUSION:

·        The methods can be directly applicable to Industry for increasing strength properties, brightness and yield in case of deinking papers.

·        Optimization of different chemicals in deinking process can be identified, so that it is easier to apply in industry.

·        Bleaching of deinking fibers can be done with a new technological method.

·      Sizing development of the deinking paper can be analyzed in different condition and optimization of sizing chemical in deinking paper can be identified.

 

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21.     https://en.wikipedia.org/wiki/Deinking

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Received on 25.10.2017         Modified on 07.11.2017

Accepted on 20.12.2017         © AJRC All right reserved