Deinking of Wastepaper By Dr. Essam Saber Abd. El –Sayed March, 2007

Deinking of Wastepaper Recycling Process Wastepaper Grades Wastepaper Procurements Repulping Screening & Cleaning Deinking Bleaching Additives in each stage

Recycling of Wastepaper Recycling of waste paper refers to the process of recovering fibers from used paper and converting them back into usable paper and paperboard. Fibers reclaimed are called “secondary fibers” Secondary fibers can be classified into: 1- Collected wastepaper, which collected from houses and markets, such as corrugated containers, newspapers and magazines 2- Industrial wastes such as trimming and cutting paper mill, over-issued papers 3- Semi-industrial wastepaper, which are collected from supermarkets, department stores, office wastes

Wastepaper Grades There are more than 80 types of wastepaper can be collected in five major categories: Mixed Paper Old Newspapers (ONP) Old Corrugated Containers (OCC) High-grade Deinked Trimming paper

Wastepaper Sources Pre- consumer Post- consumer such as trimming, clipping, cull rolls of converting and printers mills, over-issue), which is generally clean and well sorted. such as wastes from home, office, markets, which collected and baled.

Degree of Recycling There are two primary indices used to compare the level of recycling in various countries: Recovery Rate: is the amount of wastepaper recovered for reuse compared with paper consumed Utilization Rate: is the amount of secondary fibers used in paper/board production compared with the total fiber used.

Wastepaper Procurement Collection Sorting Classification Repulping Cleaning Screening Deinking Bleaching

Common contaminants in wastepaper repulping systems In-Mill Problems Typical Sources Types of contaminant Cannot be handled in conventional systems, causes defects in products Adhesives & coatings Hot Melts Difficult to remove, sticks to roll, causing sheet indentation Blocks and beads used in packaging Polystyrene foam Slow down pulper process, causes sheet product defects Laminated paper product Wet Strength Resins

Difficult to remove, causes products defects Adhesives & coatings Latex Difficult to disperse, fouls equipment and degrades products Coatings & laminates Waxes Sticks to fabrics, causes black spots in product Laminated products Asphalt Causes product defects and web breaks Vegetable & synthetic fibers Foreign fibers

Deinking process Deinking of pulp is essentially a laundering or cleaning process, where the ink is considered to be the dirt. Chemicals along with heat and mechanical energy, are used during repulping to dislodge the ink particles from the fibers and disperse them in the stock suspension. The ink particles are then separated from the so-called “grey stock” by flotation or washing techniques or by applying a hybrid process that utilizes the both separation techniques.

Surfactants Surfactants “surface active agents” are the chemicals used in stock deinking, which affect the surface tension of liquids & solids. Surfactants are molecules having a dual character, part of each molecule is hydrophilic and the other is hydrophobic. Typically, these agents are chemically modified mineral oils, where hydrophilic groups have been added to the molecular structures to make them partly soluble. There are three specific types of surfactants, are important in deinking application: 1-Detergents: to remove the ink from fiber 2-Dispersents: to keep the ink particles dispersed and prevent re-deposition onto the fibers 3-Foaming agents: to reduce the surface tension of water and to promote foam formation Other chemicals, such as caustic soda, sod. Silicate and borax are also used to enhance the action of the surfactants.

Deinking Process System Design A deinking system is designed according to the type of wastepaper used, quality of deinked stock desired and the furnish type to be deinked. A deinking system should be designed to meet the individual needs of paper mill. All systems have some basic characteristics in common. These are: Removing ink from fiber (pulping) Removing ink from stock (cleaning/screening and washing/flotation) Bleaching

(Repulping) Repulping is the first stage in the deinking process. In this stage, the secondary fiber is defiberated and the ink is removed from the fiber and dispersed. Pulping may be achieved by batch or continuous methods. Pulping consistencies are usually between 4-6%(low-consistency pulper) or 12-15% (in high-consistency pulper). The amount of mechanical energy generated by the pulper is important in determining the rate of defibering and the rate of ink removal and dispersion. The mechanical energy is dependent upon the pulper configuration and pulping consistency.

Types of Pulpers Low-consistency pulper High-consistency pulper Drum pulper Betonniere high-consistency pulper Secondary pulper

Types of Pulpers Schematic arrangement of an HC pulper (for slushing deinking materials, ONP and MGP) Interior of an LC pulper (for manufacturing of packaging paper and board)

Types of Pulpers Schematic arrangement of a drum pulper ( for low wet strength grades) Drum pulper

Cleaning and Screening Forward (conventional) centrifugal cleaners remove particulates having specific gravities greater than wood fibers. Reverse cleaners are used for removal of light contaminants. Particle size and shape have some influence on ink removal by centrifugal cleaners Following centrifugal cleaning, the stock is screened with either pressure screens or open vibrating screens. Ink removal by screening is poor because the ink particles tend to align themselves with fibers and pass through screen

Types of Cleaners * MC (up to 2 %) cleaners. For removing small heavy particles. * LC cleaner (0.5-1.5 %) for light particles. HC (2-5 %) cleaners. For precleaning for removing coarse and heavy particle that may cause damage in the processing system.

Types of Screeners Coarse screen with rotating screen cylinder Disk screen (opened)

Flotation Process After cleaning and screening, the remaining ink particles are separated from the stock by washing or flotation process. In the flotation process, a series of flotation cells is used. A flotation cell is tank supplied with air bubbles. In this process, chemicals (surfactants) are introduced during the pulping operation to promote flocculation of the ink particles and the foam, and then aerated at law consistency (typically at 0.8-1.2%). The chemistry of flotation process depend on adhering ink particles to the air bubbles. These bubbles rise to the surface as a froth and are skimmed off as rejects. A series of secondary cells is used to increase fiber yield. Ink removal effectiveness decreases as ink particle size falls below 40-50μm.

Flotation Process Floatation cell

Washing Process In the washing process, the detergents and dispersants are utilized in the pulper to remove the ink constituents from fibers, break them down, and disperse them into very fine particles. The ink dispersion is subsequently separated from the pulp, typically by a multistage dilution and thickening washing sequence to produce a clean pulp. The separation of ink is achieved during washing process by washing equipment or screens. Depending upon the type of washer, a wide range of consistencies can be used. The ink particles in this process are extremely small (less than 15μ).

Washer Machines Belt filter type washer Schematic arrangement of a Dynamic Washer

Combined washing & flotation process The objective in washing is to break the ink down into particles under 15μ, render them hydrophilic, and keep them finely dispersed. For effective flotation removal, the ink particles must form hydrophobic flocs, ideally in the size range from 30 to 60μ. In the two-stage system (washing-flotation), washing serves to remove fines and fillers along with the smaller ink particles. Washing also appears to enhance the flotation stage by removing some contaminants elements from the furnish which inhibits attachment of ink particles to bubbles.

Printing Inks components pigments modifiers vehicles

Pigments Pigments are insoluble, colored materials, within the vehicle and therefore, must be dispersed. The pigment type is determined the desired color. Dyes are soluble colored materials within the vehicle, and not generally used because of their low resistance to light and a tendency to migrate to fibers. Deinkability is not normally influenced by pigment type.

The ink Vehicle Ink Vehicle is the most important component in determining ease of ink removal. A vehicle is composed of a resin (binder), which binds pigment particles together and to the surface of the paper, and a solvent, which provides the ink with proper fluidity. Binders, when dried form polymerized films which vary greatly in their chemical resistance.

Common Binders Description Binder Rosin Ester Esterification of rosin acids with glycerol or sorbitol hardened with a condensate of phenol and formaldehyde. Rosin Ester Polymerization of unsaturated hydrocarbon fractions Petroleum Resins Reaction of polyfunctional acid with polyfunctional alcohols condensed with drying oil fatty acids (forms oil-modified polyester resins) Alkyd Resin

Common Binders Photo or electron beam initiated free radical polymerization of epoxy acrylates, urethane acrylates, or polyester acrylates. Radiation-Cured Alkaline water soluble vinyl or styrene acrylate copolymers with amine addition for alkalinity. Water-Based

Modifiers Modifiers are materials which give inks specific chemical or physical properties. Examples are waxes, plasticizers, drying agents and co-solvents. They are added in small quantities and do not impact the deinkability of inks.

Types of Ink Drying Mechanisms Ink is frequently classified according to its drying mechanism. There are four general mechanisms for drying ink: 1-Absorption 2-Evaportion 3-Oxidation 4-Radiation curing

The chemistry of Deinking The most important deinked chemical mechanisms are: Fiber Swelling Saponification Wetting Emulsification / Solublization Sequestration / precipitation Antiredeposition Dispersion

The chemistry of Deinking Fiber Swelling occurs when immersed cellulosic fibers in water or electrolyte solution. The breaking of interfiber bonds and swelling of fibers are important steps in deinking as they greatly facilitate loosening and removal of inks and coatings from fiber surfaces. Saponification involves hydrolysis of esters in aqueous alkali. This reaction will convert the ester into its component acid and alcohol. Many of the resins used as ink binder are esters and therefore can be broken up in hot alkali solution. This is one of principle reactions occurring in deinking of conventional offset and gravure inks. Phenolic modified rosin often esters can be saponified under severe conditions of pH and temperature

Wetting When a liquid surface is in contact with a solid, the molecules at interface may be more attracted to the solid than the bulk liquid. If so, the molecules tend to spread out over the solid and surface area (surface tension or energy) of the liquid is increased. This phenomenon is called wetting. In deinking, with liquid (water) and solid (ink and fiber), proper wetting allows more rapid penetration of chemicals into fiber network and ink-fiber contact area and helps ink break up and separate from fiber. Surface energies influence ink collection in flotation cells.

Emulsification and Solubilization Emulsification is the dispersion of liquid phase to another to form a significant stable suspension. Emulsification is an important chemical mechanism in deinking only when there are oils present in ink. Adsorption of emulsifying agents (surfactants) at the oil-fiber interface release the oil from the fiber (with the pigment particles) and forms an oil-in-water emulsion. Solublization, simply put, is the dissolving of substances in a medium in which they are normally insoluble. Solublization differs from emulsification in that solubilized material is in the same phase as the solution while emulsified material is a dispersion.

Peptization Peptization is the conversion of an insoluble solid to a colloidal state whereby the particles are electrically stabilized. The important of peptization as deinking mechanism is unknown. But it probably occurs, for example, as a secondary reaction following saponification of ester-based resin binders or as ink particles are mechanically and thermally broken up.

Sequestration and precipitation The presence of polyvalent cations notably calcium, magnesium, and iron- can be detrimental to the deinking process even, when nonionic surfactants are used. These cations can reduce negative surface charges on both fiber and ink leading to agglomeration and redeposition. Catioins also may act as linkages between –ve fiber and –ve ink particles. These ions inter the system in the water or paper stock and can be removed by sequestration (formation of a water soluble complex) and precipitation (formation of an insoluble precipitate).

Dispersion Dispersion is the phenomenon of adjusting the surface characteristics of particles (suspension or emulsion) to prevent reagglomeration. Adsorption of negatively charged dispersing agents (surfactant or inorganic ions) onto detached ink or emulsified oil particles causes mutual repulsion and prevents agglomeration.

Antiredeposition Antiredeposition refers to preventing the deposition of solid ink and oily particles back onto fibers. They function by sterically inhibiting the approach of ink particles to fibers and can be quite effective as wash aids in washing deinking.

Deinking Processing Aids Dosage (%of Fiber) Furnish Type Function Structure/Formula Deinking Chemical 3-5 Wood-free grades Fiber swelling Ink break up Ink dispersion NaOH Sodium Hydroxide 2-4 Ground -wood grades Peptization Alkalinity and buffering H2O2stabilization Na2SiO3 Sodium Silicates 2-5 Alkalinity buffering Na2CO3 Sodium Carbonate

0.2-1 0.2-2 0.5-2 All grades Metal ion sequestrant Ink dispersion Peptization Ink dispersion Na5P3O10 Na4P2O7 Sod. or Pot. Phosphates 0.2-2 Ink removal Wetting Emulsification Solubilizing CH3(CH2)-CH2-O(CH2CH2O) xH Ethoxylated Linear alcohol/ Alkyl Phenols Nonionic surfactants 0.5-2 Wood-free grades Ink softening Solvation C12-C14 aliphatic saturated hydrocarbons Solvents

Polyacrylate-Diisobutylene Maleic Anhydride Copolymer 0.1-.5 All grades Ink dispersion Antiredeposition Sequestration -CH2-CHC=O O-(Na+) n Polyacrylate-Diisobutylene Maleic Anhydride Copolymer Polymeric dispersants 0.5-3 Ink flotation Aid CH3(CH2)16 COONa Sodium Stearate Fatty Acid (Soap) 1-2 0.5-1 Ground wood grades Bleach Color Strip H2O2 Na2S2O4 …Cl2 ..OCl2 Peroxide Sod. Hydrosulfite Chlorine