State-Of-The-Art for Paper Recycling - Ok

8/12/2019 State-Of-The-Art for Paper Recycling - Ok

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International Conference on Science and Technology (ICSTIE) 2008

12-13 December 2008Universiti Teknologi MARA, Pulau Pinang, Malaysia

PULP AND PAPER RECYCLING PROCESS

The recycling process involves: re-pulping the wastepaper to reduce it to a fiber slurry; de-inking (separating ink

from the cellulose fibers); and finally removal of the ink particles from the stock. The fiber slurry is then turned into

paper using conventional papermaking machines. The source of recyclable fiber has been mainly newsprint andmagazine waste. It is important to have a suitable combination of both long and short fiber to yield a pulp that willproduce paper of acceptable quality. Magazine waste provides some longer fiber material (chemical wood) which

improves the overall quality to newsprint (mechanical wood) furnish.The first stage in recycling wastepaper involves re-pulping to reduce the material to fiber slurry. This was

achieved by stirring the waste in the presence of water and chemicals using a hydra pulp. During this process, fibers

can be shortened as a result of breaking (cutting). The breaking of fibers is less likely to occur if the pulps are at a

higher consistency as the action of fiber against fiber is gentler than fiber against metal pulp paddle. Ink detachment

takes place simultaneously with re-pulping. The final task is to remove the separated ink particles from the stock.

Different techniques are used to remove particles of differing size. Contraries of sizes from about 200mm diameter

and upwards are removed by screening. The pulp is passed down the screen in a circular motion and accepted fiber

passes through the mesh while rejects are collected at the bottom. One disadvantage of this method is that the slurry

thickens towards the bottom of the basket and the efficiency drops to such an extent that only the top part of the

screen is functional.

Then, the pulp was clean by spinning it around in large cone-shaped cylinders. Heavy contaminants likestaples are thrown to the outside of the cone and fall through the bottom of the cylinder. Lighter contaminantscollect in the center of the cone and are removed. This process is called cleaning.Sometimes the pulp must undergo

a pulp laundering operation called deinking to remove printing ink and sticky materials like glue residue and

adhesives. Papermakers often use a combination of two deinking processes. Small particles of ink are rinsed from

the pulp with water in a process called washing. Larger particles and stickiest are removed with air bubbles in

another process called flotation. During flotation deinking, pulp is fed into a large vat called a flotation cell, where

air and soap like chemicals call surfactants are injected into the pulp. The surfactants cause ink and stickiest to

loosen from the pulp and stick to the air bubbles as they float to the top of the mixture. The inky air bubbles create

foam or froth which is removed from the top, leaving the clean pulp behind.

PULP AND PAPER RECYCLING TECHNOLOGIES

The prime objective of recovered paper recycling is to utilize the fibers contained in pre or post-consumed recoveredpaper. Non-fibrous components, whether they derive from paper or are added during the processing or the use of

paper, should be removed at the highest degree possible to avoid quality defects in the produced papers (specks,

holes) and production process faults (e.g. wet web breaking) [9]. Using current technologies, it is more costly to

manufacture products from waste materials compared to virgin materials. New technologies for converting waste to

high quality products should be develop. The conventional recycling process has two drawbacks; it is more

expensive and releases more carbon dioxide than manufacturing new paper. Consumers tend to pay more to

purchase recycled paper, pay in their time to separate paper from other waste for recycling and may pay for the

separate collection of recyclable material.

In this paper, it describes studies on pulp and paper recycling in five problem areas: paper and fiber sortingtechnologies, deinking and contaminant removal, pulp bleaching technologies, restoration of papermaking propertiesof recycled fibers, and performance characteristics of recycled paper.

(a) Paper and Fiber Sorting Technologies

Approximately half of wastepaper is generated by offices; the other half, by households. About 60% of the office

wastepaper can be readily and reliably sorted into standard office paper grades. The remainder of office paper as

well as household paper is mixed and contaminated. Successful recycling requires clean recovered paper. The paper

must be keep free from contaminants, such as food, plastic, metal, and other trash, which make paper difficult to

recycle. Recycling centers usually sort the paper by grade, or type of paper. At some level of mixing and

contamination, manual methods of sorting paper become impractical. The technology necessary to recover paperfrom very mixed and contaminated sources has not been developed.


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(b) Deinking and Contaminant Removal

Wastepaper contains adhesives, fillers, inks, dyes, metal foils, plastics, and dirt. Current separation methods, which

separate particles on the basis of size and density, are not adequate for recycled fibers. Many wastepapers contain

contaminants that are similar in size and density to the fibers, such as nonwettable synthetic adhesives ("stickies").

New approaches are needed to separate these contaminants from recycled fiber. Biological processes can also beused to separate paper fibers from ink and other contaminants. Biological processes generally facilitate the removalof contaminants, but they can also affect fiber drainage, strength properties, yield, and slime accumulation [8].

(c) Pulp Bleaching Technologies

New environmental regulations are shifting production away from chlorine-based bleaching processes. Technologies

designed to meet new environmental regulations for the bleaching of virgin fiber will likely be applied in recycling.

However, the unique properties of recycled fibers will require considerable modification of these technologies as

well as development of new technologies. Studies are addressing four fundamental obstacles to effective and

environmentally safe bleaching of recycled fibers: feedstocks with mixed lignin content, photoreversion, color

stripping, and physical aggregation of cellulose [8]. Selected bleaching agents can be used to determine the extent to

which diffusion and mass transfer slow or impede the bleaching process. In practice, accessibility might be

improved using chemical or biochemical treatments, some of which may overlap with treatments used to restore

papermaking properties.

(d) Restoration of Papermaking Properties of Recycled Fibers

The final stage of papermaking is drying the sheet at relatively high temperature, hardens the surface of fibers and

stiffens their internal structure. These effects must be reversed if the fiber is to be reused for papermaking.

Hardening of the surface limits inter fiber bonding, and internal stiffening reduces the conformability of the fibers.

Both effects can limit the consolidation of the paper web. Recent literature indicates that the fundamental problem

encountered when making paper from recycled fibers is loss of relative bonded area. Traditional methods of treating

recycled fibers with alkali or mechanical beating have been only partially successful in restoring the original

papermaking potential of the fibers. Changes in structure affect the void volumes within the fiber cell wall. Re-establishment of the original volumes is critical to restoring fiber flexibility and conformability.

(e) Performance Characteristics of Recycled Paper

Papermakers are able to produce a remarkable array of products with very different properties by controlling the

furnish, additives, and process. When postconsumer fiber is introduced into fine paper grades, control of one of

these variables is lost: the furnish of recycled fiber is a mixture of various species pulped by various means. If the

product is to remain consistent, the other variables-additives and process must be adjusted to compensate for

changes in furnish. To obtain consistent products, papermakers must be able to characterize all essential

performance aspects of a particular product or grade of paper. At present, characterizing subtle differences that

affect paper performance challenges the limits of our technology. Changes in the surface energy of secondary fibers

and the presence of contaminants can significantly affect the friction properties of the paper product. Reduction ofthe coefficient of friction can cause problems with roll-winding, printing, sheeting, and feeding of photocopiers.

Neither the measurement of friction nor the mechanisms of its effect are well understood.

PROPERTIES OF PAPER RECYCLING

During the past two decades, numerous studies have been conducted on the potential of papermaking from recycled

fibers. Most studies have shown that the strength properties of fibers and paper are reduced upon recycling. The

effects of drying are presumed to be the main factors in reducing the strength properties of recycled fibers. Drying

influences fiber strength, fiber swelling and bonding potential, which are the important factors to the strength of

paper made from recycled fibers [3].

It seems that strength properties of recycled paper, such as tensile and bursting strengths, which aredependent on fiber bonding, are dramatically decreased with recycling. However, for strength properties of recycled


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paper where fiber bonding is not the main factor, such as tear strength, recycling seems to have a beneficial effect up

to a certain level of recycling [14; 2].

The type of wood from which the pulp is derived and the lignin content of the original pulps also appear to

have different effects on the changes in recycled pulp properties. The tear factor of recycled bleached kraft

hardwood pulp was found to decrease, while that of bleached kraft softwood pulp increased with recycling [15].

Recovering the bonding potential of dried fibers is not as easy as those of virgin fibers (never dried fibers).Many attempts have been made to increase the suitability of recycled fibers for papermaking. These include varioustechniques of beating and chemical treatment of recycled fibers. There are four possible ways to recover the loss of

bonding of recycled fibers: (1) beating and refining, (2) chemical treatment, (3) blending with virgin fibers, and (4)fiber fractionation [6].

Two basic approaches have been utilized to improve the properties of recycled pulp: mechanical treatments

and chemical treatments. The approaches were designed to obtain a more fundamental understanding of the

mechanisms of regeneration of the properties of recycled fibers and paper. The term mechanical treatment is used to

indicate that no chemical treatments were involved; only beating of the pulp in a PFI mill [13].

Chemical treatment of pulp is another method to increase and regain the bonding potential. Various

chemical treatments have been evaluated for both virgin and recycled pulps. Alkaline-based solutions are the most

common chemicals utilized for improvement of the bonding potential of pulps [7; 4; 12; 5]. The influence of alkali

treatment for the development of strength properties of the recycled pulp is apparently dependent on the type of

alkali and reaction condition applied to the pulps. Most investigators have suggested that alkali treatment influences

the swelling capacity of the fibers, which is a very important factor in terms of the bonding potential of the fibers.

CONCLUSION

It is well known that waste paper came from various sources such as newspapers, magazine papers, office and

printing papers, and boxes. Each has different type of fiber quality. Mixing all these different type of quality paper

will reduce the purity of the highest quality fiber. With proper segregation of paper types according to its existing

fiber quality, different recycled paper quality can be produced with the right mixing instead of using virgin paper to

top up the fiber quality.

The basic recycling process is similar to the paper making process. Sorted wastepaper is cleaned by de-

inking and then broken down in large quantities to form a "porridge". The fibres are then refined and additivesincluded to give particular qualities to the end paper. Virgin pulp is added at the end of the pulp making process.

Two basic approaches have been utilized to improve the properties of recycled pulp: mechanical treatments

and chemical treatments. For mechanically treated pulp, the tensile and bursting strength of the never dried pulpdecreased with increasing consistency of beating. Tear strength increased with increasing beating consistency. The

chemical treatments were selected to maximize the swelling effects on cellulose to improve bonding ability. The fact

that the treatments did not alter and even reduced the strength properties, such as burst and tensile, seems to indicate

that other factors are important to the bonding of recycled fibers.

The production of recycled paper has less overall environmental impact than producing paper using all new

material, when all production activities are taken into account. Recycled paper production does use less energy, less

water and creates less pollution. However substantial upgrading of low quality waste, could mean that the

environmental advantages of recycling are reduced or lost.

REFERENCES

[1] Chalmers Website, (2008). http://www.chalmers.se/gmv/ Accessed on 24 March 2008

[2] Chaterjee, A., Kortschot, M, Roy, D. N. and Whiting, P. (1993) Tappi J. 76(7), 109115.

[3] Ellis, R. L. and Sedlachek, K. M. 1993. Recycled Versus Virgin Fiber Characteristic: A Comparison. In: Secondary

Fiber Recycling. (Spangenberg, R.J. ed). Tappi Press. Atlanta, Georgia, p. 7.

[4] Freeland, S. Caustic Soaking: A Pilot Plant Trial. In: Tappi Proc. 1995 Recycling Symposium,p.117123.

[5] Gurnagul, N. (1995) Tappi J. 78(12), 119.

[6] Howard, R. C. (1990)J. Pulp Paper Sci. 16(5), J143J149.


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[7] Katz, S., Liebergott, N. and Scallan. A. M. (1981) Tappi J. 64(7).

[8] Laufenberg, T. L and Abubakr, S. Expanding Research Horizons: USDA Forest Service Initiativefor Developing Recycled Paper Technology.USDA Forest Service Forest Products Laboratory

[9] Onussert, H. (2006). The influence of adhesives on recycling. Resources, Conservation and Recycling. 46;168181

[10] Pulp and Paper Information Centre Website, (2008). http//www.ppic.org.uk Accessed on 22 March 2008.

[11] TAPPI - The Leading Technical Association for the Worldwide Pulp, Paper and Converting Industry (2001). How to

recycle paper?.

[12] Waterhouse, J.F. and Liang, Y.X. (1993). Improving the Fines Performance of Recycling Pulps. In: Tappi Proc. 1995Recycling Symposium, p.103116.

[13] Wistara, N. and Young, R. A. (1999). Properties and treatments of pulps from recycled paper. Part I. Physicaland chemical properties of Pulps. Cellulose 6: 291324.

[14] Wyk, W. V. and Gerischer, G. (1982). Paperi ja Puu 64(9), 526533.

[15] Yamagishi, Y. and Oye, R. (1987).Japan Tappi 35(9), 33.

State-Of-The-Art for Paper Recycling - Ok

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