Analyzing contaminants in OCC:Wax or not wax?By B. Cao and O. Heise

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Pulp & Paper Canada T 82 106:4 (2005) ❘ ❘ ❘ 41

carbon paper and hot melt adhesives, and for thepreparation of printing ink, is not a true wax.Rather, it is a mixture of alkanes. Despite the dif-ference in their chemical structure, paraffin wax inmodern industry and natural wax bear a strongresemblance in their function. In cosmetics, it pre-serves moisture in human faces; in the fruit indus-try, wax prevents moisture loss from oranges andapples; in the packaging industry, it provides amoisture barrier and maintains structural integrity.

Paraffin wax consists of a mixture of homolo-gous normal alkanes in substantially a straight-chain configuration. Soft paraffin wax (meltingpoint 40-42°C) is used for the impregnation ofpaper, and hard paraffin wax (melting point 50-52°C) is used to manufacture candles and for cer-tain impregnation purposes.

Unlike paraffin wax, microcrystalline wax pos-sesses an isoparaffinic structure. The microcrys-talline wax is tougher and more plastic, and has ahigher melting point (60-80°C). Microcrystallinewaxes have a higher viscosity in the molten statethan ordinary paraffin waxes of the same molec-ular weight, and their density is also greater.

Polymers have been used for many years toimprove the properties of waxes [2]. Glass-likelow molecular weight resins are used to improvetack. Higher molecular-weight resins or plastics,such as polyethylene and various copolymers ofethylene with propylene, vinyl acetate, isobutylacrylate or ethyl acrylate, are added to improveadhesion, toughness and flexibility. Elastomers orrubbers used alone, or more often in conjunctionwith resins, offer further improvements in prop-erties, especially seal strength, grease resistance,tensile strength, low-temperature flexibility, watervapour transmission rate and viscosity control.

The amount of polymer additions ranges from1 to 25%. The molecular weight of these poly-mers ranges from 33,000 to 450,000, and can beas high as 1.6-million. Ethylene-vinyl acetatecopolymer (EVA) is the most common polymericadditive used in wax-based coatings. EVAs withsoftening points up to 204°C are generally used.One example of such an application is curtain-coated paperboard. Polymeric material isrequired here to achieve a good holdout, andthus minimize penetration into a porous fibre

N MANY occasions we are told that anOCC mill has a wax problem. Whenasked further about the symptoms ofthe problem, mill personnel oftenpoint at that some culls are marred by

many dark spots, often called bleedthroughs.Although bleedthroughs may be caused by certain wax contaminants, most of thebleedthroughs, as been proven [1], are caused bypolymeric contaminants, not by wax. As the strat-egy of a recycled fibre-processing system hingeson the nature of the contaminants, it is importantfor people to correctly recognize the type of con-taminants with which they deal. This paperintends to analyze different types of contaminantsin OCC pulp and their respective effect on paperand board quality. Following that analysis, threetest methods are proposed to quantify the con-taminant level in OCC pulp. These three meth-ods complement each other and give a full pic-ture of the pulp quality.

PROPERTIES OF WAX & WAX-BASED HMAIn the early days of papermaking, beeswax andother saponifiable animal and vegetable waxeswere dispersed by a reaction with an alkali, andadded to the beater either alone or with rosin.These true waxes are esters of long chain fattyacids with long-chain alcohols. They occur widelyin nature and serve a number of functions inplants and animals. Beeswax is a high molecular-weight material used by bees to form a honey-comb. Spermaceti is found in the head of thesperm whale, and probably helps to regulate theanimal’s buoyancy for deep diving. The carnaubaplant secretes a waxy material that coats its leavesto prevent excessive water loss by evaporation;this function is very similar to what papermakersdo with wax in sizing or coating.

CH3(CH2)29-O-CO-(CH2)24CH3 — a componentof beeswaxCH3(CH2)33-O-CO-(CH2)26CH3 — a componentof carnauba wax

In contrast to these waxes, paraffin wax, widelyused in the paperboard industry to manufacture

O

Abstract: The contaminants in OCC pulp consist of a diverse group of polymeric and non-poly-meric materials. The author described the effect of main types of contaminants on paper and boardquality. It is revealed that each type of contaminant causes different problems affectingpaper/board quality and machine runnability, and therefore needs to be dealt with differently. Fol-lowing the analysis of contaminants in OCC, three quantitative methods are proposed to determinethe over-all contaminant level in OCC pulp.

B. CAOVoith Paper Fiber Systems DivisionAppleton, WIbangji.cao@voith.com

substrate. It also improves the toughnessof the coating so it can remain intact dur-ing shipping and handling. Curtain coat-ed wax is applied as a thin film on the sur-face of paperboard.

Hot-melt adhesives (HMAs) are anoth-er major application of petroleum waxes.HMAs are similar to curtain coatingsexcept that they contain a higher level ofEVA and resins, and consequently have amuch higher softening point and melt vis-cosity than curtain coatings. Waxes areminor components in HMAs and are nec-essary to lower viscosity, therefore avoid-ing an unworkably high viscosity for HMA-applying equipment. Coatings based onthese high molecular weightethylene/vinyl acetate (EVA) copolymers,combined with petroleum waxes andmodifying resins, can be formulated toprovide excellent water vapour barrierproperties, heat-sealability, flexibility, andgloss [3]. These properties, coupled withgood handling characteristics on packag-ing equipment, enable EVA-based coat-ings to meet many of today’s packagingrequirements. Other adhesives and plas-tics may also contain a minor amount ofwax as rheology modifiers. Table I lists thecomposition and specific gravity for sever-al HMAs produced by 3M Corp.

Diagram 1 summarizes properties of dif-ferent types of wax-containing materials,and provides a guideline for further studyof their effect as contaminants in fibres.Paraffin Wax Causes Low Angle of Slideand Strength Loss: Solid wax is a fragilematerial. As the temperature approachesits melting point, wax becomes even easi-er to break. In a hydraulic repulper, wax isreadily fragmented as mechanical andthermal energy is applied [4,5,6]. Whenthe pulping temperature reaches its melt-ing point, violent agitation forces liquidwax to mix thoroughly with water to forman emulsion. Often a dispersant is addedto wax to keep it stable before beingapplied to paperboard. The dispersant inthe repulped stock will also keep the waxemulsion stable. In this emulsion, wax isin a dispersed phase and water is in a con-tinuous phase. Upon cooling, waxremains dispersed due to the presence ofwater media and shear forces. The size ofwax particles average approximately 5µm.

These fine wax particles are evenly dis-tributed in fibre slurry during sheet for-

mation, and some of them are retained bythe filtration mechanism and physicalentrapment. As the paper sheets runthrough the drying cylinders, which havea temperature of approximately 177°C, allwax particles melt in the fibre network.The liquid wax spreads quickly in the cel-lulosic fibre network. Its mechanism isdescribed as follows:

Wax liquid spreads on the surface offibre as to increase the interface betweenwax and fibre, and the interface betweenwax and air. The ease of this process isdetermined by spreading coefficient S:

–�GspreadingS = ————— = �sv – (�sl + �lv) (1)A

In the equation (1), Gspreading is the freeenergy change due to spreading, �sv is theinterface energy of fibre-air, �sl is the inter-face energy of fibre-wax, and �lv is theinterface energy of wax-air. If S≥0, the liq-uid spreads spontaneously over the solidsurface. If S<0, the liquid does not spread;it makes up an angle with the solid surface.This angle is such that the total surface freeenergy of the system is at the minimum.

In the wax-fibre-air system encounteredin a paper machine, wax liquid has a verylow surface tension, approximately 8.6-24.3 mJ/m2, measured by TF Ling [7]. Onthe other hand, the cellulosic fibre has avery high surface energy, about 48mJ/m2

[8]. In this circumstance, the molecularadhesion between fibre and wax liquid isgreater than the molecular cohesion ofwax molecules; therefore, the wax liquideasily spreads on the fibre surface.

Once the dried sheets are cooled down,the wax re-solidifies within the fibre net-work. Since it is uniformly distributedthroughout the whole sheets, paraffin waxdoes not show up collectively in a driedsheet. Paper sheets contaminated withparaffin wax are whiter and opaque thanwax-free sheets. This is because the pres-ence of wax increases the number of inter-faces in a fibre network, therefore increas-ing the light scattering coefficient. Thesolid wax is greasy and slippery. Even asmall amount of wax in paper sheets cancause the angle of slide to drop quickly. Forpaper and converting mills, the decrease ofangle of slide can be a serious issue.

According to William McDonnell [9],the surface friction of the outside ply of a

linerboard sheet is a critical characteristic.It not only affects the productivity of sub-sequent converting operations, but alsothe stability of the loaded boxes as well.The top ply must exceed a minimum spec-ified coefficient of friction. The coeffi-cient of friction of linerboard is deter-mined by the tangent angle at which thesample begins to slide. If this angle is toolow, efficient conversion of paperboardand box utility is restricted.

Figure 1 shows the angle of slidedecreases rapidly as wax content in thepulp increases to about 4%, and levels offafter 5% wax. As the amount of wax in thepulp increases, more fibre surfaces arecovered by wax. It appears that 5% is thethreshold at which all fibres are coveredwith wax. The minimum angle of sliderequired by a linerboard mill is about 25°.The wax level at 25° is 1.8%. Subtracting0.3-0.7% for other solvent extractives infibres, the wax content tolerable in a liner-board mill is 1.1-1.5%.

In addition, the presence of paraffinwax weakens sheet strength properties.Hydrogen bonds are responsible for thestrength of fibre-to-fibre bonding. Suchbonding requires intimate contactbetween fibres during sheet formation. Inorder to bring two fibre elements into con-tact at the molecular level, the compactingpressure must reach 100-200 atmosphericpressures, which is difficult to achieve byany mechanical means. However, theinterfacial energy caused by water is ableto achieve such high compacting pressure.The surface tension acting on fibres isexpressed approximately as:

��P = 2 (—) (2)

X

In which �P=compacting pressure,�=surface tension of water and X=thick-ness of water film between to fibres.

In the emulsion of water-wax, the sur-face tension of water � is reduced by waxas it suppresses the tendency of watermolecules to escape from the liquidphase, which is the driving force for sur-face tension. As a result, the compactingpressure is reduced proportionally. Inaddition, the fibres whose surface is coat-ed by wax lose their ability to form hydro-gen bonds. Only weak van der Waals

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DIAGRAM. 1. Properties of wax-containing materials.

Type of Hot Melt 3778 3762 3738 3764 3792

Application Wood Corrugated Corrugated Cartons CorrugatedComposition

EVA, % 50-60 40-50 50-60 50-60 60-70HC Resin, % 20-40 30-40 20-30 25-35 30-40PE, % 3-7 10-20 10-20 5-10 -Parafin Wax, % - 10-20 1-10 1-5 -

Specific Gravity 0.95 0.95 0.95 0.95 0.97

TABLE I. Composition of 3M HMAS.

forces exist between such fibres. The over-all results are reduced fibre bonding areaand specific bonding strength. The influ-ence of wax on sheet strength is shown inFig. 2. The maximum loss in tensile, burstand tear indices is between 25 and 45%.The fact that tensile, burst and tearstrength decrease simultaneously suggestsa weakened fibre bonding in the network.It is interesting to note that the levelingoff point for both the angle of slide andstrength is at about 5% wax content.Curtain Coated Wax Causes Bleed-throughs: Although curtain-coated wax iscalled wax, as much as 60% of its ingredi-ents are not paraffin wax. The balance ofthe material is EVA and tackifying resins.Polymeric material is required to improvethe toughness of the coating so it canremain intact during shipping and han-dling. The polymer itself is a tough plasticbecause its chains are long enough to con-nect individual stems together within acrystallite lamella by chain folding. Thechains also wander between lamellae, con-necting several of them together. Theseeffects add strong covalent bond connec-tions within wax, in which only weak vande Waals forces hold the chains together.In addition, some portions of the polymerare amorphous. The chains in these por-tions are rubbery, imparting flexibility tothe entire material. Wax, in contrast, is100% crystalline, and therefore is brittle.

Toughness makes curtain wax more dif-ficult to disperse during repulping. Thecurtain coating usually has a melting pointbetween 82 and 93°C; therefore, it softensbut does not melt during normal pulpingtemperatures. Curtain coatings will breakdown into small pieces of wax chips. Thesewax chips are thin and pliable, allowingthem to escape through fine screens.

Unlike cascade wax, the escaped cur-tain wax chips show up as bleedthroughsin dried paper sheets, giving them a dirtyappearance. The dark spots arise from aslow diffusion of hydrocarbon moleculesin the curtain wax. As polymer is added towax, the melt viscosity and flow resistanceof the molten wax increases rapidly due tothe entanglement of polymer chains. Fur-thermore, the diffusion of polymermolecules is sterically retarded withinfibre cell walls. Since both polyethyleneand low molecular weight hydrocarbons

are of the same chemical nature, theytend to aggregate with each other. As aresult, these types of wax particles formdark spots in dried sheets. Figure 3 showsthe bleedthroughs caused by curtain waxin a handsheet.Polymeric Contaminants are PrimarySources of Bleedthroughs and Stickies:Both cascade-coated and curtain-coatedboards are very easy to identify. They areusually sorted out at collection sites andkept from entering the recycling stream.Still, the aesthetic quality of the boardproducts using OCC furnish has beensteadily declining in recent years. Most ofthese paper products are marred withdark spots. These dark spots result fromthe melting of micro plastics, fragmentedhot melt adhesives, fine stickies and otherpolymeric contaminants; therefore, thedark spots are termed bleedthroughs. Anypolymeric contaminants with a meltingtemperature of less than approximately177°C could generate bleedthroughs.Though the majority of these contami-nants can be removed with a standardfibre processing sequence, many fine con-taminant particles will remain in the treat-ed pulp. These fine particles may eitherbe brought in by the contaminated OCC,or generated by the fragmentation of larg-er pieces during the recycling treatment.At an elevated temperature (of approxi-mately 177°C) in the board machine dry-er section, most of the polymeric contam-inants will melt and migrate into fibrevoids. At the spot occupied by the lique-fied contaminant, a dark bleedthrough isformed. It gives the finished paperboard adirty appearance. Figure 4 is a picture ofbleedthrough after it has been enhancedwith a black, water-soluble dye.

Failure to remove these fine contami-nants, along with the increasing use ofOCC, has caused deterioration in the aes-thetic quality of paperboard. The currentsolution to minimize the effect ofbleedthroughs is to disperse the fine poly-meric contaminants instead of removingthem. As a result, most of these fine con-taminants will come back to the recyclingsystem when new board products aremade from OCC. Apparently, the stan-dard OCC fibre-processing sequence isnot designed to eradicate the issue ofbleedthroughs [10]. The contaminants

can escape any of the current separationprocesses, and could survive many cyclesbefore being degraded. This will lead tothe accumulation of bleedthroughs.

Hot melt adhesive (HMA) contains asignificant amount of paraffin wax, but itspolymer component and tackifying resindominate its physical behaviour. The poly-mer imparts the bulk strength to the adhe-sive; the resin provides surface wetting andtack. The wax plays the role of plasticizer tosoften the adhesive and gain processability.The wax consists of small and non-volatilehydrocarbon molecules that are compatiblewith polyethylene, and capable of dissolvingin the polymer. The dissolved moleculesseparate polymer chains and weaken theintermolecular forces, hence making therelative motion easier for macromolecules.The addition of wax lowers the glass transi-tion and softening temperature.

As its softening point is lowered, HMAis susceptible to plastic flow undermechanical stresses. At the press section ofa paper machine, HMA contaminantsundergo irreversible flow or creep, fillingthe voids within felt web. At the same time,the contaminants are forced into directcontact with fibres. The tackifying resinand the polar acetyl groups in vinyl acetatemake these contaminants very stickytowards the wood fibre substrate. Conse-quently, they pick holes in wet sheets,cause sheet breaks, and reduce the sheetdryness out of the press section. Pluggingof wires likely occurs at the vacuum boxes,couch roll and other units that apply amechanical force in any manner.

Although the contaminants do not usu-ally cause serious runnability problems at

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Pulp & Paper Canada T 84 106:4 (2005) ❘ ❘ ❘ 43

FIG. 1. Impact of the wax content on

angle of slide of paper.

FIG. 2. Impact of wax content on

paper strength.

FIG. 3. Bleedthroughs caused by cur-

tain-coated wax.

FIG. 4. Image of bleedthroughs after

being enhanced with black, water-sol-

uble dye.

the dryer section, they do so in many con-verting plants. For instance, in manufac-turing brown towels viscous hot melts stickto the embossing plate, spoiling theembossing operation. Another example isGypsum board: water-based latex does notpaint over these hydrophobic spots well.

ANALYSIS OF CONTAMINANTS IN OCCSolvent Extraction: Paraffin wax is a mate-rial with a low melting point and high sol-ubility in many solvents. In the past, thewax content in paper samples was conve-niently measured using trichloroethane(TCE) extraction (TAPPI T 405). Howev-er, chemical suppliers have stopped pro-ducing these chlorinated compoundsbecause of toxicity. Using TCE for waxextraction has been outdated by bothASTM and TAPPI. As part of TAPPI Pro-cess and Product Quality Division’s effortto find a new, safe solvent for wax mea-surement, we compared the extractionresults of four different solvents: Methylethyl ketone (MEK), Hexane (HEX), Ace-tone (ACE), and TCE. Each solvent wasused to extract two types of wax: cascadecoated wax in corrugated medium, andcurtain coated board. Extraction curvesare shown in Figs 5 and 6.

As indicated by the charts, MEK has aslightly higher extraction power than TCEfor both cascade and curtain-coated sam-ples; therefore, it was chosen as thereplacement of TCE. Hexane’s extractionfor paraffin wax yields the lowest resultsand acetone is not a proper solvent for cur-tain wax extraction. As a matter of fact, cur-tain wax does not dissolve in acetone. It wasreleased as chips from the paperboard inacetone. These chips were included in theextractives when the extraction time wasrelatively short (30 minutes). As extractionprogressed, the chips disappeared and theextraction yielded lower results. It isassumed that acetone interfered with somecomponents in the curtain wax.

FTIR spectrum of the extracted mate-rial showed that the extraction with TCE,MEK and HEX did not change the paraf-

fin wax and curtain wax chemically. Whenextracted with acetone, paraffin wax andcurtain wax showed very similar FTIRspectrum, indicating that only paraffinwax was in the extracted material and oth-er ingredients in curtain wax wereexcluded when acetone was used.

The test data showed that the majority ofextractable material was removed from sam-ples within 30 minutes when MEK was used.Another 30 minutes would insure the near-ly complete extraction of wax. The pro-longed extraction will inflate test resultsbecause other wood extractives are removedfrom fibres. These wood extractives exist infibre lumens, making them much more dif-ficult to extract than wax. The extractiontime should be limited when the purpose isto determine the wax content.

When MEK extraction is applied tosamples containing a substantial amountof wax (>3%), it yields meaningful data.When it is applied to regular OCC sam-ples, the data must be carefully interpret-ed. Many contaminants, such as hot meltadhesives and plastics, interfere with thewax extraction. In addition, virgin kraftpulp contains 0.3 to 0.7% extractives. Thebaseline extraction of OCC samples isconsidered approximately 1%.

MEK is a flammable solvent, so safetyprecautions must be applied when it isused for wax extraction.Quantification of Bleedthroughs: Thepolymeric contaminants, which generatebleedthroughs, are usually fine particleswith an average equivalent diameter ofapproximately 170µm. Many of these con-taminants have a specific gravity close toone. Therefore it is very difficult to sepa-rate them from fibres. In addition, theamount of polymeric contaminants isoften very low in pulp at the end of a fibre-processing system. Tests of bleedthroughsrequire good sensitivity and repeatability.

The method described below quanti-fies the bleedthroughs in OCC pulp [11].The method takes advantage of fusion andhydrophobicity of polymeric contami-nants. Handsheets were first made frompulp samples according to the TAPPI stan-

dards. The basis weight of the handsheetsis adjusted to 60 g/m2. The handsheetsare then pressed between two hot platensunder pressure of 8-16 psi. The tempera-ture of the hot platens is set at 149°C. Afterten minutes, polymeric contaminants meltand diffuse into a fibre web.

At the spot occupied by a contaminantparticle, a bleedthrough is formed. Usuallythese bleedthroughs appear as dark spots inthe light background of OCC paper sheets.Looking at the sheets against a light source,the dark spots appear semi-transparent ifthe basis weight is low. After hot pressing,the handsheets are dyed in water-solubleblack ink to enhance the contrast betweenbleedthroughs and sheet background. Sincecellulosic fibres are highly hydrophilic, thearea free of contaminants will absorb water-soluble ink and become black, while thebleedthroughs are water-repellent andremain undyed. The air-dried handsheetsare then scanned with an image analyzerthat has the capacity to detect light con-traries. The bleedthroughs are quantified asparts per million of the sheet area. Test of Stickies (TAPPI T277): Because ofits packaging and shipping function, con-tainer-board brings a large amount ofsticky contaminants into the recyclingprocess during its consumer cycle. Theorigin of stickies in OCC pulp can betraced to one of the following materials:

Bar code labels, box sealing tapes, boxsealing hot melts, self-adhesive shippinglabels, self-adhesive strapping tapes, kraftpackaging tapes, filament reinforced pack-aging tapes, preprinted warning labelsand self-adhesive packaging tapes. In addi-tion, plastic bags, strings and cushionmaterials may become very tacky underthe elevated temperatures, though they donot belong to adhesives under normalconditions. For a paper machine, it doesnot have to be an adhesive to be consid-ered a sticky contaminant, for any poly-meric contaminant is a potential sticky.

The chemical origin of stickies in OCCis even more diverse than its material ori-gin, since each adhesive formulation usu-ally contains several ingredients: poly-

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FIG. 6. Solvent extraction of curtain-coated wax.FIG. 5. Solvent extraction of impregnated medium.

mers, tackifiers, rheology modifiers, fillersand stabilizers. The chemical compositionof these materials may contain several ofthe following basic components: styrenebutadiene rubber (SBR), ethylene vinylacetate (EVA), polyvinyl acetate, polyvinylacrylate, polyethylene, polyisoprene,polybutadiene, polyamide, polyurethane,polyvinyl alcohol, polyvinyl ether,polyester, acrylic acid ester, block copoly-mers, wax, and natural or modified woodresins. As a minor component in adhe-sives formulation, wax is used mainly inhot melt adhesives to control its process-ability and melt viscosity. A pure wax orwax-dominated formulation does not con-stitute stickies, since wax is a low molecu-lar weight, low-melt viscosity material.

Testing stickies is an important but diffi-cult task for papermakers. Testing stickiesin OCC is even more difficult, becauseOCC pulp contains many non-tacky con-taminants such as wet strength flakes. Beinga diversified group of materials, the stickycontaminants possess different physical andchemical properties, such as solvent solu-bility, surface energy, glass transition tem-perature, degree of polymerization, crys-tallinity, degree of cross-linking, etc. Thismeans it will not be feasible to utilize any ofthese properties to detect and quantifystickies. Methods like deposition andextraction are unreliable because of theunpredictable nature of stickies.

Stickies are defined as the tacky sub-stance in pulp and water that deposits onvarious parts of a paper machine such asthe felt, couch roll and drying cylinder.Therefore, by definition, the commoncharacteristic of all stickies is tackiness.The method employed in TAPPI T277takes advantage of this tackiness to detectand quantify stickies. The pulp sample isfirst screened with a laboratory screen with0.15-mm slots. The debris is then retainedon a black filter paper by filtration. Afterfiltration a stickies marking paper is placedon the filter paper with its coating side

against the debris. Sandwiched betweentwo blotter papers, the debris, togetherwith the stickies marking paper, is heatedand pressed under 95°C and 0.8 bar for 10minutes. As the temperature increases, thetacky materials start to soften and flowunder the pressure.

One side of the stickies will anchor onthe filter paper and the other side willpick up the coating from the stickiesmarking paper. Once the marking paperis peeled off, stickies will show up as whiteparticles on a black background. The oth-er non-tacky debris is washed away fromthe filter paper. The constant contrastbetween the stickies and its backgroundallows easy detection and quantificationwith an image analyzer. The followingseries of picture in Fig. 7 illustrate the test-ing procedure graphically.

CONCLUSIONS• The contaminant in OCC pulp is adiverse spectrum of polymeric and non-polymeric materials. Each type of con-taminant causes different problems topaper quality and machine runnability,and needs to be dealt with differently. Thecorrect recognition of contaminants isessential to the effective design of thefibre processing sequence.

• Paraffin wax is rarely an issue for regu-lar OCC mills because the cascade-coatedboard is usually sorted out at collectionsites and kept from entering the recyclingstream. The presence of paraffin waxcauses dramatic decreases in the angle ofslide, tensile strength, burst strength andtear resistance. However, paraffin waxdoes not cause any bleedthroughs onboard/paper sheets.• Unlike paraffin wax, curtain-coated waxis not mechanically dispersible under thenormal pulping temperatures. The curtainwax is released from paperboard as waxchips. Melting them causes bleedthroughs.Both paraffin wax and curtain wax can betested with methyl ethyl ketone extraction.• Fine polymeric contaminants are theprimary source of bleedthroughs in OCCmills. The current standard design of anOCC fibre-processing sequence does notremove these fine contaminants effective-ly. The bleedthroughs in OCC pulp canbe quantitatively determined with a heatsetting and dyeing method.• The origin of stickies can be traced backto many materials. Any polymeric contami-nant is a potential sticky. Stickies should betested based on tackiness, the commoncharacteristic of all stickies. The stickiespick-up method takes advantage of this tack-iness to detect and quantify stickies. Themethod is standardized as TAPPI T 277.

LITERATURE1. McEWEN, J.G.E. Wax Contamination in PaperRecycling: Understanding Wax Chemistry and Recy-cling Waxed Papers. Paper Recycling Challenge. Vol. 1.Ed. M. Doshi M. and J.M. Dyer. City: Doshi & Associ-ates, 1997, 118-127 (Year).2. BRILLINGER, J.H. Elastomers in Hot Melt Formu-lations. Tappi J. 52(9):1672-1674 (1969).3. LAMAR, S.T., D’ADDIECO, A.A. Barrier Propertiesof Paper Coated with Blends of Ethylene/VinylAcetate Copolymers and Wax. Tappi J. 48(7): 385-391(1965).4. DOELLE, K., WITEK, W., HEISE, O., CAO, B. Flota-tion Machine with Hot Air for a Fiber Suspension andMethod of Using Same. US Patent 6,395,131 (2002).5. DOELLE, K., WITEK, W., HEISE, O., CAO, B.Flotation Machine with Cold Air for a Fiber Suspen-sion and Method of Using Same. US Patent 6,394,279(2002).6. HEISE, H., CAO, B. Method of Removing Wax fromCellulose Fiber Used in a Fiber Suspension for aPapermaking Machine. US Patent 6,228,212 (2001).7. LING, T.F. Agglomeration Tendency of Contami-

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FIG. 7. Stickies test procedure according to TAPPI T277.

Reference: CAO, B., HEISE, O. Analyzing contaminants in OCC: Wax or not wax? Pulp & PaperCanada 106(4): T82-86 (April, 2005). Paper presented at the 6th Research Forum on Recycling inMagog, QC, on October 1 to 4, 2001. Not to be reproduced without permission of PAPTAC.Manuscript received on August 5, 2001. Revised manuscript approved for publication by theReview Panel on July 30, 2004.

Keywords: WASTE PAPERS, CORRUGATED BOXES, CONTRARIES, POLYMERS, WAX,ANALYSIS, STICKIES, OCC, TESTING, HYDROPHOBICS, HOT MELT.

Résumé: Les contaminants des pâtes de VCO sont composés de diverses matières polymèreset non polymères. Nous avons décrit l’effet des principaux types de contaminants sur la qualitédu papier et du carton. Nous avons déterminé que chaque type de contaminant cause des prob-lèmes différents en matière de qualité de la pâte et du carton et d’aptitude au passage surmachine, et ils doivent donc être traités différemment. Après l’analyse des contaminants dans lesVCO, trois méthodes quantitatives sont proposées pour déterminer le degré global de contami-nants dans la pâte de VCO.

nants in Recycled Fibers. Tappi J. 81(3):161-165(1998).8. LUNDQVIST, A., ODBERG, L., BERG, J.C. SurfaceCharacterization of Non-chlorine-bleached PulpFibers and Calcium Carbonate Coatings Using InverseGas Chromatography. Tappi J. 78(5):139-148(1995).9. McDONNELL, W.T. Wax: A Source of Low SurfaceFriction in Kraft Recycled Linerboard. Tappi J.76(10):31-36(1993).10. OLIVER, H., CAO, B. System and Method forRemoving Bleedthroughs from Old Corrugated Con-tainer Fiber Pulp. US Patent 6,425,982 (2002).11. CAO, B., OLIVER, H. Test Method for Determin-ing Bleed-throughs in Old Corrugated ContainerFiber Pulp. US Patent 6,589,389 (2003).

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