chapter ii pulp, paper, and fiber products

CHAPTER II

Pulp, Paper, and Fiber Products

CHAPTER Ill

Pulp, Paper, and Fiber Products

Summary and Conclusions

Pulp and paper manufacturing is movingtoward the production of higher quality pulpsthat require less wood input per ton of pulp andpaper produced. Increased energy costs, in-creasing raw material costs (for both round-wood and sawmill residues), a market that nowemphasizes printability and other nonstrengthfactors, and the availability of immenseamounts of less expensive hardwood timberhave prompted the U.S. pulp and paper indus-try to consider more energy-efficient and ma-terials-efficient manufacturing technologies.

The adoption of mechanical pulping technol-ogies could reduce the amount of fiber requiredto produce a ton of paper from about 2.5 tonsof wood, for the kraft chemical pulping proc-ess, to about 1.05 tons for thermomechanicalpulping. With this reduction, it is estimatedthat each future increase of 2 percent in pulp-ing capacity would necessitate an increase ofonly 1.7 percent in wood fiber feedstocks.1

These potential increases in pulping efficiencyand fiber yield can effectively extend the Na-tion’s usable wood supply, reducing the likeli-hood of raw materials shortages and relaxingthe pressures on the shrinking U.S. timberlandbase. Expanded use of hardwood species thatare presently underutilized may further extendthe domestic timber supply.

Pulping technologies like organosolv holdprospects for the industry to become a netenergy producer. The organosolv process mayalso permit utilizing hardwood species and ob-taining high fiber yields with little sacrifice inproduct strength. Such processes are still in thedevelopmental stages but may be commerciallyavailable in 25 years. Meanwhile, the pulp andpaper industry could reduce the amount of en-

‘G. Styan, “Impa{.t of North American Tlrnber Supply on In-novat ions i n Paper Ttx:hnology, “ pa~}er Tra~~ Journal, VC)I. 164,M a y 30, 1980,

ergy required by increasing the use of mechan-ical pulping and expanding the use of recycledpaper. In addition, the efficiency of chemicalpulping may be increased by adopting pyrolytictechnologies for the recovery of spent pulpingliquor, autocaustisizing to reduce the energyrequired in the lime-kiln process, and using an-thraquinone as a catalyst for chemical kraftpulping to increase fiber yields.

Press-drying technology, while still in devel-opmental stages, shows promise for both re-ducing the amount of energy required in thepapermaking process and enabling the use ofhardwood species not currently used in largequantities. In some respects, the quality of thepaper produced by this method exceeds thatof unbleached kraft paper produced by conven-tional processes. It may also afford an oppor-tunity for the U.S. pulp and paper industry tocapitalize on a growing export market in liner-board and other heavy-duty packaging ma-terials.

Advanced research and development (R&D)on improving the strength and stiffness of pa-per could lead to development of structural fi-ber products able to compete with a numberof metallic, ceramic, and plastic materials. Inaddition, paper may be combined with othermaterials such as plastics, coatings, and syn-thetic fibers to produce composite materialswith superior qualities.

Although plastics have made significant in-roads in certain types of packaging, and havesignificantly displaced paper sacks for light-duty uses, paper still commands a major pro-portion of this market and will probably con-tinue to do so. Moreover, increases in energycosts could improve paper’s competitive posi-tion relative to petroleum-based plastics, whichrequire larger energy inputs in production. Thepaper industry could further strengthen its

67

68 ● Wood Use: U.S. Competitiveness and Technology

competitive position if it continued to adoptexisting energy-efficient technologies.

Electronic telecommunications technology,on the other hand, could have significant im-pacts on demand for printing and writing pa-per in the future. While the magnitude of itseffect on paper is yet uncertain, the introduc-tion of advanced electronic devices such aselectronic filing (the “paperless” office), videomagazines, electronic newspapers, and video

catalogs and directories may increasingly af-fect the use of paper now and during the nexttwo decades. Recently, the use of word proc-essors and office copying equipment has in-creased the demand for paper products, a trendthat may decline as electronic communicationsgain increased acceptance in offices. In thefinal analysis, the long-term effects of telecom-munications technologies on paper require-ments are unknown,

Introduction

Profile of the Pulp and Paper Industry

The United States has the largest per capitapaper and paperboard consumption in theworld, averaging more than 600 pounds annu-ally. It is also the world’s largest producer ofpaper and paper products, accounting for ap-proximately 35 percent of the world’s total out-put. The U.S. pulp and paper industry is ninthin size of tons produced and 11th in gross as-sets among the domestic manufacturing indus-tries. In 1981, U.S. production of pulp, paper,and paper products was estimated at $82.1 bil-lion (current dollars).’

Raw Materials

In 1978 the pulp and paper industry used ap-proximately 77 million tons of pulpwood (ovendried). Forty-four percent of this came fromchips and sawmill residues, which are woodwastes from the manufacture of lumber andother solid wood products. About 26 percentof the pulpwood used in 1978 was hardwood.(Trends in wood use in the past 40 years havebeen toward increased use of hardwood spe-cies and increased reliance on chips and saw-mill residues.) In addition, the U.S. pulp andpaper industry used approximately 15 milliontons of recycled wastepaper for pulp and pa-per production in 1978.3

‘IJ. S. D e p a r t m e n t of (lommerCe, 1982 ]n~~st~ja] uut]~~k(Washington, D. C.: U.S. Government Printing Office, 1982), p. 39.

‘Joan E. H uher, The A’line Guide to the Paper Industr}r (Fair-fie]d, NJ.: (Jharlcs H. Kline & (j{),, 1980) , pp. (j6-67,

The pulp and paper industry also uses aboutone-quarter ton of chemicals for each ton ofpaper or paperboard produced, ranking sixthamong all industries in dollar value of chemi-cal products purchased. It is also the largestuser of water for processing among all manu-facturing industries. Finally, the industry is oneof the leading industrial consumers of energy,using roughly 7,2 percent of the Nation’s in-dustrial energy requirements and 2,8 percentof the total energy used in the United States.Approximately half of the energy used by theindustry is produced internally from wood res-idues and other waste products. Because of thelarge energy requirements and the sensitivityof production costs to energy prices, the pulpand paper industry has become an industrialleader in energy conservation and cogenera-tion (internal generation of electricity fromsteam heat),

Product Demand

Demand for paper and paper products isclosely tied to economic growth and disposableincome levels. Although year-to-year fluctua-tions occur, correlating with economic trends,the industry is relatively free from the cyclicalvariations experienced by other primary indus-tries such as mining, metals, and solid woodproducts.

Capital

The pulp and paper industryally high capital requirements

has exception-for plant and

Ch. Ill—Pulp, Paper, and Fiber Products • 69

equipment, Capital investment currentlyranges from $350,000 to $1 million per installedton of daily capacity, depending on a mill’s de-sign and whether the investment is an additionto the existing mill or a new facility.4 The pa-per industry invested $6.8 billion in capital ex-penditures in 1980; however, $369 million, or5 percent, was spent on pollution controlequipment that did not increase production ca-pacity.’

Industry Size and Production

With over 4,000 f i rms employing about626,000 workers, the pulp and paper productsindustry is an important component of the U. S.economy. It produces over 14,000 different pa-per products, and its potential for developingnew and even better paper and fiber productsin the future is high. At the same t i me, moreefficient manufacturing processes could re-duce energy use and lead to increased use ofpresently underutilized, but prevalent, hard-wood species.

It is estimated that paper products accountfor almost three-fourths of the wood-basedsales of the top 40 firms in the forest productsindustry.6 While the pulp and paper sector con-sists of a large number of competing firms, the10 largest firms manufacture over half of thepulp, paper, and paperboard products pro-duced in North America. In addition, a num-ber of the major pulp and paper manufacturersproduce a variety of secondary products, in-cluding solid wood items, containers, writingpapers, and sanitary paper products (table 22).Fifteen companies that produce both paper andsol id wood products are prominent among thewood-based industries, but together they ac-counted for only 24 percent of all wood-basedsales in the United States in 1978.7

In 1976, the South produced 67 percent ofthe Nation’s wood pulp. Southern forests areparticularly attractive to the industry becauseof the abundance of both softwoods and hard-woods, The pulp and paper industry has ex-panded its capacity in the South in recentyears; while the South’s share of total pulp pro-duction was only 48 percent in 1947, it is nowover two-thirds, The West produced 17 percentof the Nation’s wood pulp in 1976. The remain-ing 14 percent was produced i n the East andin the North Central States. B

While pulpmills are located near raw mate-rials, the manufacturing sector of the industry,which makes containers, bags, sanitary prod-ucts, and stationery, is concentrated near themarkets. Thus, the New England Middle At-lantic, and North Central States produce 62percent of all paper products. Much of thetimber resource in these regions is hardwood,which has not been used extensively for paperproduction in the past. Wood pulp productionin these regions currently constitutes only 16percent of total U.S. wood pulp production.

Uses of Pulp, Paper, and Paperboard

Total U.S. pulp production has been pro-jected to increase from 53.2 million short tonsin 1981 to 54.8 million short tons in 1982. However, the actual volume may be lower as a re-sult of the 1981-82 recession. g In addition to thedomestic products used, approximately 4.3 mil-lion short tons of pulp were imported in 1981,primarily from Canada. Pulp exports totaled3,7 million tons, most of which was shippedto Europe, Mexico, Japan, and Korea. The total53.8 million short tons of pulp used were con-verted into over 66 million tons of paper andpaperboard. Imports of primary paper and pa-perboard products were about 8 million tonsin 1981, while exports slightly exceeded 4 mil-lion tons,

Wood pulp is converted into a variety of pa-per products (table 23). The major uses of pa-per, which accounts for 49 percent of the wood

70 . Wood Use: U.S. Competitiveness and Technology

-“ I

vK

I

Ch. Ill—Pulp, Paper, and Fiber Products ● 7 1

Table 23.—U.S. Production of Paper and Paperboardin 1981 and Projected for 1984 (thousand tons)

1981- 1984a-

Paperboard ... ... ..-.. ., . : 14,558 15,360Kraft fiberboard ... ... . . 1,067 1,140O t h e r k r a f t p a p e r b o a r d . , . . . 4 , 7 1 7 5,070Bleached paperboard ., ... ... . 3,926 4,100Recycled paperboard . 7,070 7,150

T o t a l p a p e r b o a r d . , . . . . . . 3 1 , 3 3 8 33,020

Paper:Uncoated free sheet . . . . . . . . . . . . . 7,882 8,720Coated free sheet and groundwood . 4,951 5,340Uncoated groundwood ... 1,440 1,540Bristols and other ... ... ... . 1,530 1,580

Total printing and writ ing . . 15,803 17,180

Newsprint ... ... . . ... . . . . 5,238 5,730

Unbleached kraft ., . ... ... ... . 3,891 3,760

Bleached regular and industrial . . 1,603 1,670

Tissue ., . . ... ... . . . . ... 4,485 4,730

Total paper ., . . ... ... ... . . . 31,020 33,070

Total paperboard and paper ... 62,358 66,090aMorgan Stanley estimates

—

SOURCE Thomas P Clephane and Jeanne Carroll Linerboard Industry Outlook(New York Morgan Stanley & Co 1982) p 25

pulp produced, are for printing and writing pa-pers [50.9 percent), newsprint (16.9 percent),tissue (14.5 percent), and packaging (17.7 per-cent). Over 51 percent of U.S. wood pulp pro-duction is converted to paperboard (a stiff,heavy paper). Linerboard, which is kraft paper-board used for boxes, shipping containers, andpackaging, accounted for 46.4 percent of thepaperboard produced in 1981. Overall, packag-ing materials (both paper and paperboard)made up 59 percent of all paper and paper-board produced in the United States, and wasone of the most rapidly expanding pulp uses.

Since the price elasticity of demand (thechange in demand resulting from a change inprice) for paper products is generally small, therecent decline of relative prices has probablyhad only a small positive impact on apparentpaper consumption.10 The U.S. Department ofCommerce projects shipments of primary pa-per and paperboard products to rise at the rateof 3 percent annually for the next 5 years. Mar-ket projections through 1986 suggest a steadyincrease in domestic and worldwide demand

1 O(; a ] ~u la t j(j ns 1)F. the K ldd~r, Peilhodj’ E c o n o m i c s G r~up ill-d ic. ate that the relative price elastic it~’ of demand for paper isapproxi miitely 0.5 percent.

for paper products in general. Demand for pri-mary paper and board products is expected tobe exceptionally strong. Economic factors af-fecting demands for communications, packag-ing and shipping papers, and boards, however,will ultimately determine actual demand levels.

The most promising markets during the en-suing 5 years are expected to be for linerboardand high-quality printing papers. An increaseof 6 percent in the trend line of 1982 linerboardexports is forecast by some analysts,ll and thedemand for high-grade printing and publish-ing papers is projected to increase at an annualrate of about 7 percent.12 Demand for bothprinting paper and linerboard is expected toexpand at rates twice that for products of thepaper industry overall. While domestic con-sumption will probably increase gradually inresponse to a stronger economy, the demandfor exports is expected to increase even more,in response to expansion of the industrial econ-omies of the People’s Republic of China, Japan,Malaysia, Indonesia, the Philippines, Taiwan,and Korea.

Advanced Paper Materials

The development of stiff, durable paper, withstrength characteristics currently achievableonly at the experimental level, offers futureprospects for new structural building products,Paperboard has been tested for use as sheath-ing and wall modules in buildings with mixedresults. 13 The effects of moisture on the dimen-sional stability and stiffness of the paperboardis a major factor limiting the usefulness of pa-per as a structural material. New high-strengthpapers with protective coatings, coupled withinnovative designs for paper-based structuralmaterials, are a possibility, But considerableR&D remains to be done prior to commercial-ization.

I] Thomas p, C]epha ne and Jeanne Ca rrol ], Linerboard Indus’-try Outlook (New York: Morgan Stanley & Co,, 1982], p. I Z.

IZCorp~rate Strategies, “A Narrowed Boise Cascade F’ocuscson Paper, ” l?usiness il’eek, Apr. 26, 1982, p. 81.

13’’ Emergency Housing for $2,500, ” Technology Re\Fie~t”, Ma\’/June 1982, p. 86. “Paperboard Houses Now Approved for all Ex-posures by FHA, ” Paper Trade Journal (Aug. 23, 1971], p. 53;“Paper Houses Buyers, ” Chemica) Engineering, Sept. 8, 1969,RP 76-71.

72 . Wood Use: U.S. Competitiveness and Technology

Wood pulp may be converted into paperproducts ranging in character from superab-sorbent fluffy tissue to extremely hard, board-like materials. Wood pulp’s versatility resultsfrom the ability to vary paper’s stiffness overa wide range. Wood fibers are extremely flex-ible, strong, and durable. When brought intoclose contact, they form a durable fiber webas a result of hydrogen bonds, strong bondswhich provide the strength and stability of pa-per. Hemicellulose acts as an adhesive betweenthe fibers and adds strength.

Stiffness is the major quality that makes pa-pers so suitable for boxes, shipping containers,and, possibly, structural building materials. Al-though strength is also important, it is morefrequently lack of stiffness that limits thechoice of materials for these products. Becausecellulose fibers attract water, moisture can af-fect paper’s structural integrity by softening thefibers and reducing their stiffness, Tests inmodifying paper to enhance stiffness and mois-ture resistance, performed at the U.S. ForestService Forest Products Laboratory (FPL), havedemonstrated that super-strength paper may,on a weight basis, be capable of matching theperformance of other solid materials like solidwood, aluminum, and steel.14

The major factors affecting stiffness that aresubject to control by the papermaker are fiberorientation, density and fiber bonding, and

IAv. setterho]m, ‘ ‘Factors That Affect the Stiffness of Paper,The Fundamental Properties of Paper Related to Its Uses, vol.1, F. Bolam (cd.) (London, England: The British Paper and Paper-board Industry Federation, 1976), pp. 253-266.

shrinkage control during the drying cycle. *sThe prospects for improving paper stiffnessthrough the use of synthetic resin additives arenot considered as promising as improved bond-ing and fiber orientation in the papermakingprocess.

Researchers at FPL hypothesize that anelastic modulus of approximately 1.5 millionpounds per square inch (psi), with a specificgravity of 0.4, could be achieved in paper inwhich the fibers are parallel and shrinkage iscarefully controlled during drying. This levelof stiffness is approximately equivalent to thatof wood parallel to the grain at the same spe-cific gravity. Laboratory tests have producedpaper sheets of specific gravity of 0.75, witha tensile strength of 38,000 psi and an elasticmodulus of 3.8 million psi.16 These values sub-stantially exceed the specific strength and stiff-ness-to-weight ratios of all common structuralmaterials, including solid wood. Only certaingraphite and boron fiber composites surpassthe strength of this “super paper” at the spe-cific gravity tested. Laboratory researchersconclude that paper can be produced that isstiffer and stronger than the wood from whichit is made, If high-strength papers can be de-veloped that are capable of maintaining stiff-ness and dimensional stability in high humid-ity, they may be used for a range of structuralapplications now being served by wood, plas-tics, or metals—e.g., housing, furniture, andcontainers,.

IsIbid., p, 266.lelbid., p. 260.

Role of Paper and Cellulosic Materials in the U.S. Material Mix

Competition with traditional paper commod-ities for U.S. markets comes primarily fromtwo areas: plastics and electronic communica-tions. Competition from plastics is often in theform of substitution of plastic products forpaper products and, occasionally, compositeproducts made from paper and plastics, Elec-tronic communications, on the other hand,

have the potential for displacing a share of thepaper market by reducing the need for writing,copying, printing, and business forms. So far,however, electronic communications has prob-ably resulted in greater consumption of paper,owing to increased use of word processors,high-speed computing systems, and inexpen-sive office copiers.


The impact of competition from plastics and products, in contrast to linerboard and paper-the electronics media on paper materials will boards used in shipping containers, will be seri-vary among paper products. Newsprint, writ- ously affected by competition from plasticing and printing papers, business forms, paper products and the electronic media. The print-bags, and wrapping papers constituted 47 per- ing and writing paper sector, which constitutescent of paper consumption in the United States one-third of U.S. paper consumption, will likelyin 1979 (table 24). Some anticipate that these experience the greatest impact from the expan-

Table 24.—Uses, Grades, Production, and Consumption of Paper Products in the United States in 1979

ApparentProduct ion consumption

Market Grade (thousand tons) Percent (thousand tons) Percent

Newspapers . . ... . . . ... , . ... . ...Magazines, directories, catalogs . . . . . . . . . . .

NewsprintUncoated

groundwoodCoated papersUncoated book

4,062

1,5304,526

7,868376125

1,114

3,934

1,791

4,525

29,851

14,076

1,127

4,721

4,023

4,88331,631

3,466—

6

27

12<1<1

2

6

3

11,215

2,2544,640

16

37

11<1<1

2

6

2

6

54

18

1

7

5

1142

5—

100

Magazines, annual reports, other periodicals . .Books . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . .Commercial printing, envelopes, business

forms, Iables, duplicator covers, and text . . Writing andrelated

Thin paperCotton fiber

7,913391126

1,116

Cigarettes, carbonizing condensers . . . . . . .Bond, writing, other business, and technical .,Tabulating index, tag and file folder,

post card ... ... . . . . . . . . . . . . . . .Wrapping, bag, sack, shipping sack . . . . . .

Bleached bristolsUnbleached kraft

packaging andindividualconverting 3,937

Bleached bags, wrapping glassine,greaseproof ., . . . . . ... , . . . . . . . . . . . . . . Other packaging

and industrialconvertingpaper

Special industrialpaper

1.729Industrial converting . ... . . . . . . . . . . . . . .

Sanitary tissue papers, waxing, and wrappingtissues . . . . . . . . . . . . . . . .

Total paper ... . . . . . . . . . . . . . ... .Facing for corrugated or solid fiber boxes . . . .

7

46

Tissues 4,514

37,835

12,611Unbleached kraft

Iinerboard 22Tube, can, drum, file folder, shipping

containers . . . . . . . . . . Other unbleachedkraftfiberboard 2 1,050

Recycled corrugating medium, chip and fillerboard boxes, partitions and dividers . . . . . Semichemical

paperboard 7 4,737Folding cartons, milk cartons, paper plates,

cups, posters . . . . . . . . . . . . . . . . Solid bleachedpaperboard 6 3,310

Folding cartons, setup boxes, gypsumwallboard facing . . . . . . . . . . . Recycled

paperboard 1249

7,53329,241Total paperboard ., . . . . . . . . ... . . . . .

Construction products, insulating board,binder, and shoe board . . . . . . . . . . . . . . . . . . Building and wet

machine board 5—

100

3,763(462)Other . . . . . . . . . . . . . . . . . . . . . . . . . .

Total paper ., ... . . . ... , ... ... , . . . . . . .— 64,947 70.340SOURCE Adapted from G Boyd Ill and H Dudley, Paper Industry Outlook for 1980 Through 1982, Part // (New York K!dder , Peabody & Co 1980) p 10


sion of electronic communication if telecom-munications technology is accepted by thebusiness community and home use expandssignificantly in the future. Plastic substitutesfor paper bags, wrapping papers, and miscel-laneous office supplies could displace 10 per-cent of the paper consumed in the UnitedStates annually,

Competition From Plastics

The use of low-density polyethylene film(LDPE) for packaging, wrapping, and sacking,and high-density polyethylene film (HDPE) forprinting and wrapping paper, is a comparative-ly recent trend that began during the past dec-ade and continues to expand at a steady rate.Plastics claimed only a l-percent share of thegrocery sack market (small sacks used for in-dividual items) in 1979, but within 2 years ex-panded to 5 percent of the market. The plasticsindustry projects that plastics could capture asmuch as 25 percent of the grocery sack mar-ket by 1985,’7 but, according to some analysts,the penetration of plastics into the traditionalkraft paper markets will probably be selective,For example, the grocery bag market (larger,multiwalled, heavy-duty bags) may be less vul-nerable to inroads by plastics, at least duringthe intermediate term (10 to 15 years).l8

Several factors will determine the futurecompetitiveness of plastics in relation to pa-per products: 1) relative production costs, in-cluding raw material (resin for plastics andwood, and chemicals for paper), labor (in gen-eral, the paper industry is more labor-inten-sive), and energy consumption; 2) rate of tech-nical innovation; and 3) consumer acceptance.

Sack/Bag Market

Plastics’ share of the merchandise bag mar-ket was estimated to be 35 percent in 1981, anincrease of 10 percent over the previous year,Investment analysts at Morgan Stanley & Co.estimate that plastic bags will control 60 per-cent of the merchandise bag market by 1985.19

“Clephane, p. 18.InIbid., p. 17.lgIbid., p. 16.

Production of 275,000 tons of finished bags an-nually account for only 5 percent of the totalproduction of unbleached kraft paper. MorganStanley estimates that by 1985, merchandisebags will require no more than 3 percent of thetotal production of unbleached kraft paper pro-duction.

Large grocery bags consumed 12 percent(467,000 tons) of the unbleached kraft paperproduced in 1981, Small grocery sacks ac-counted for 95 percent of the 1.3-million-tontotal grocery sack market in 1981 and used ap-proximately 34 percent of the unbleached kraftpaper produced during that year. Until recent-ly, plastics were not considered to be seriouscompetitors of kraft paper for the grocery bag/sack market; however, some analysts now pre-dict that plastics may be able to capture rapidlyan increasing and significant share of the mar-ket, The paper industry confirms that plasticsnow compete at prices ranging from $0,029 to$0.031 per sack and sell for 10 to 15 percentless than unbleached kraft sacks. The majorplastic sack producers include several oil com-panies and chemical companies: Mobil, Exxon,and Union Carbide,

One reason for plastics’ current success incompeting with kraft paper in the bag and sackmarket is the availability of low-cost resins.Another is technological developments in poly-ethylene that permit substantial reduction inplastic thickness and volumes without sacrific-ing strength. For example, development of theUnipol process for making linear, low-density,polyethylene resin in 1979 constituted a ma-jor breakthrough for the plastics industry be-cause it required considerably lower capital in-vestment and consumed less energy per unitof resin produced.

Paper currently possesses properties that aresuperior to plastics as a material for bags andsacks. The rigidity of paper sacks enable themto stand freely for filling in grocery and retailstores. To compensate for lack of sidewall rig-idity, plastic sacks must be mounted in racksfor ease of filling. Although such technologydoes not yet exist, it might eventually be pos-sible to develop a rigid-wall plastic sack capa-ble of competing economically with paper


sacks. The conversion from LDPE to newerlow-density polyethylene film could provideeven greater price advantages for plasticsacking.

Multiwall Sacks

One major segment of the paper sack mar-ket that has not yet been seriously challengedby plastics is the multiwall, bulk shipping sack.Plastics have not made significant inroads inthis sector because the strength properties re-quired put plastics at a cost disadvantage rela-tive to kraft paper. Plastics currently occupy10 percent of the multiwall sack market, andsome industry analysts assume that this mar-ket penetration will remain stable over the longterm unless unforeseen technological develop-ments occur. Product developments in the pulpand paper industry may reinforce paper’s shareof the multiwall sack market. For example, St.Regis Paper Co. recently introduced StressKraft, a superior-strength paper permitting a20-percent reduction in the weight of the pa-per used for multiwall sack construction.20

Multiwalled sacks consumed approximately 26percent of the unbleached kraft paper pro-duced in 1981.

Liquid Containers and Packaging

Plastic containers for liquidnificant gains in competition

have made sig-with glass and

coated-paper containers. Plastic l-gallon milkcontainers now dominate the market, althoughmost smaller l-quart and l-pint containers con-tinue to be coated paper. Technological innova-tion accounts for the current inroads of plasticsin the packaging sector, yet plastics have stillcaptured only a small proportion of the packag-ing and container market. Because plastics arepetroleum derivatives that are not biodegrad-able, and in some cases may produce toxicfumes if incinerated, plastic packaging prod-ucts have met opposition from environmen-talists. 21

The market for tissue wrapping papers andglassine and parchment papers has not beensignificantly penetrated by plastics, althoughplastic bakery bags and cereal box liners arein wide use, The major limitations to the useof plastics in these areas are primarily linkedto the difficulty of adapting automatic packag-ing machines for the new materials. HDPFshave properties similar to the cellulose filmsand may some day challenge conventional pa-per materials in this area.

While plastic and aluminum foil trays havesignificantly challenged paperboard fiber traysfor packaging meats, fish, and prepared andfrozen vegetables, recent trends in microwavecooking (which cannot use aluminum foil con-tainers and requires heat-resistant receptacles)have resulted in a new generation of oven-re-sistant packaging. Polyester coatings have beenjoined with molded paper trays to create a com-posite product suited for microwave cookingconditions. 22

A number of composites, which combine pa-per with plastics and metals, provide a prod-uct superior to those made with one material.Among these are collapsible plastic bags insidepaperboard cartons equipped with a spout fordispensing liquids, thermoplastic-coated paper-boards for water-resistant food containers,paper meat trays coated with plastics, paper-boards treated with clay-adhesive mixtures andbonded with metal foils, and paper cartonslaminated with plastic foams.

Printing and Writing Papers

Plastic films have not significantly displacedprinting and writing papers, except for special-ized uses. The properties of paper (printability,flexibility, wearability, and price) are wellsuited for printing, recordkeeping, businessforms, magazines, and books. The durabilityof plastics (e. g., in Mylar and waterproof pa-pers) makes them useful for transparent repro-ducible graphics, children’s books, and outdooruse, However, the cost of printable plastic filmsis approximately twice that of the highest

‘z~lr, l,onl~ i re, 4’ I’al)crboar(l Packages fOr ot’ens,’” Fm[i Ellglneering, ]an~]ary I $)78, [). 6 2 ,


grades of paper.23 Paper industry analysts be-lieve the probability is low that plastics will beable to displace paper in general business andcommercial use, except for the highly special-ized applications named above.

Synthetic Fibers

The major petroleum-based synthetic fibersthat compete with rayon and acetate are thepolyesters, nylons, acrylics, and olefins. In1968, the worldwide volume of cellulosic man-made fiber produced was about the same asthat of noncellulosic manmade fibers (3.9 mil-lion tons).24 Since that time, the noncellulosicfibers have dominated the artificial fiber mar-ket. This trend may continue, although the mar-ket shares for rayon and acetates appear tohave stabilized. Some predict that a slight re-surgence in the use of rayon may occur if pe-troleum prices increase significantly.

Improvements in the viscose rayon processor the development of new processes that couldreduce the cost of rayon manufacture may alsoreinforce the market position of cellulosic prod-ucts. Some claim that the rayon industry hassuffered from a reduction in R&D in the 1950’sand 1960’s, the period when petroleum-derivedsynthetics displaced rayon as the predominantmanmade fibers.

The rayon and acetate industries, however,consider their major competitor not to be thepetroleum synthetics but natural cotton fibers,Cotton and rayon have similar properties withregard to moisture absorption and other wearcharacteristics, making possible developmentof improved, cottonlike rayon fibers that aredirectly substitutable for cotton. The rayon in-dustry sees an opportunity to expand its mar-ket without meeting competition from petro-leum synthetics, based on the forecast thatworldwide demand for cotton will increase at———-— —

“’(Where Plastic Papers Stand in Printing, Bags and Tissues, ”Modern Plastics, March 1973, p. 55.

Z4Committee on Renewab]e Resources for Industrial Materials(CORRI M), Fibers as Renewable Resources for Industrial Ma-teriais [Washington, D. C.: National Academy of Sciences, 1976],p. 234.

a rate exceeding the capacity of the agriculturalindustry to meet the requirements. ’s

Competition From Electronic Technologies

Recent developments in large-scale, inte-grated circuitry are revolutionizing the com-munications and information fields by reduc-ing the size of computers and microprocessors,expanding their capacities and flexibilities, re-ducing costs, and increasing availability to awider range of potential users.26 Through theuse of satellite communications, microwave,and interfacing devices on home television re-ceivers, electronic communications may belinked with large centralized information sys-tems that are capable of providing a wide rangeof user services. Further developments in op-tical digital-disk technology (a specially coatedplastic disk on which information is encodedby a high-powered laser beam) may enable thepermanent storage and relatively cheap retriev-al of immense amounts of information.27 Fun-damental research on new concepts of datastorage and retrieval may pave the way in thefuture for even greater expansion of informa-tion technology.

Achievements in telecommunications tech-nology during the past two decades offer anumber of opportunities for improving thespeed and flexibility of communications, Elec-tronic mail is being considered by the U.S.Postal Service and private firms as a way tospeed textual communications and eliminatethe need for handling and physically transport-ing mail.28 Some foresee electronic filing lead-ing to the paperless office.29 Video magazines,which may be transmitted directly into the

Z5c; . DaU], o p . Cit., P, 84’z6LJ.S. congress, office of Technology Assessment, COmputer-

Based National Information Systems: Technology and PublicPolicy’ Issues, OTA-CIT-146 (Washington, D. C.: U.S. GovernmentPrinting Office, September 1981), pp. 3-12.

“C. Goldstein, “Optical Disk Technology and Information, ”Science, vol. 215, Feb. 12, 1982, p. 862.

“J, Free, “Electronic Mail: Good-bye to Paper?” PopularScience, September 1980, pp. 78-141.

‘e’’ Electronic Filing to Threaten Cut Size Paper Markets, ” Fi-ber Market News, No. 72, Dec. 14, 1981, p. 1,


home via satellite and conventional televisionreceiver, are in the early stages of develop-ment.30

Television-adapted versions of the phone di-rectory, retail catalogs, and other merchandis-ing devices, which can be viewed on home tel-evisions, are currently being evaluated forpublic use. 31 Also, a number of major newspa-per publishers are interested in producing elec-tronic newspapers; in the United Kingdom atleast three such teletexts are already operat-ing.32 Futurists consider as long-range pros-pects the use of vast central information sys-tems—’’hypertex capableable of retrieving, dis-playing, and manipulating information from“grand libraries” through personal consoles. 33

Such broad-scale application of electroniccommunications could affect dramatically theuse and demand for paper in the future. Al-though telecommunications has experiencedrapid growth during the past decade, its appli-cation for office and home use is still in its in-fancy, Thus, uncertainties regarding the rateof commercialization and public acceptanceand forecasts of its impacts on paper must beconsidered speculative. While there is littledisagreement among analysts that electroniccommunications may ultimately displace theneed for some writing and printing papers, thetiming and extent of the impacts are subjectsof debate.

Euro-Data Analysts, a British-based marketconsulting group specializing in the paper,board, and packaging industry, forecasts a ma-jor shift from the use of paper toward increasedreliance on electronic media.34 Over the longterm, Euro-Data considers it likely that the de-veloped countries will achieve a nearly paper-

30’’Tips on Tiipe: (;assette Magazines Arrive, ” Time, June 14,1982, p. 78.

314’ Paper Chases the EIectroni{; Age, ” Bosjness Week, Apr. 5,1982, pp. 112-115,

32K. Edwards, “The Ele(;tmnic Newspaper, ” CommunicationsTomorrow (Bethesda, ~ld,: World Future Society, 1981), pp.54-59.

“H. Freedman, “Paper’s Role in an E]ec,tronic World, ” Com-munications Tomorrow’ (Bethesda, Md,: World Future Society,1981), pp. 60-65.

34Eu rO-Data Analyst S, The Impact of Communications Tech-nologies on llemand for Printing and Writing Papers (Ashtead,Surrey, U. K.: Euro-Data Analysts, 1980),

less society as the rate of commercializationof electronic communications accelerates. Eu-ro-Data forecasts that during the current dec-ade, paper will lose a share of the market tothe electronic media through video telephonedirectories, office communications, telex, videobooks, video newspapers, consumer maga-zines, and electronic funds transfers.

The American Paper Institute (API) sees im-mediate competition with the electronic mediain electronic fund transfers, office reproduc-tions that require less paper, electronic mail,and electronic storage and microforms .35 Be-yond 1985, API anticipates competition devel-oping in direct-mail advertising; voice messagesystems that would reduce the requirementsfor envelopes and business forms; expandeduse of home video catalogs and directories;video publication of periodicals; interactivevideotext, which might reduce book publish-ing; and video systems displaying time-criticalnews, which could displace some newsprint.

By 1995 and beyond, portable handheld vid-eo displays could displace printed magazines,books, and newspapers (table 25). API notesthat the electronic media accounted for over60 percent of the total communications ex-penditures during the 1970’s. If the trend con-tinues, its share could exceed 70 percent by theyear 2000, while the paper-based media’s sharemay drop to less than 30 percent. 36

Other analysts agree that electronics technol-ogy will probably reduce the demand for print-ing and writing papers during the next decade,International Resource Development, Inc.(IRD), a technology consulting firm, sees homevideo as potentially flattening the growth in de-mand for paper directories and catalogs within6 years.37 IRD projects that by 1991, electronicfiling could reduce demand for office paper by300,000 tons per year (5 percent of current of-fice consumption). Data Resources Inc. (DRI)estimates that home video systems could startaffecting newsprint demand by 1985.38 If elec-

ssAmerican Paper ] n st itute, Information Technolog~’ and pa-per Demand (New York: API, 1981], p. 52.

j~Ibid“’’Paper Chases in the Electronic Age, ” op. cit., p. 112.‘eIbid.


Table 25.—New Information Technologies and Their Potential Impact on Paper Construction

Paper end-use categories/relevant information techniques Paper end-use categories/relevant information techniques

Commercial business and printing papers:. Printing papers.”

—Advertising: direct mail— Home video information (vid-eotex and teletext) may open new avenues for advertis-ing and could thereby adversely impact print-based ad-vertising, including direct mail. Timeframe: beyond 1985.

—Printing: financial and legal— Expanded use of wordprocessors and intelligent printer/copiers will encouragemore in-house production of forms. Electronic fundstransfers will continue to grow, subtracting from the useof printed forms in financial transactions.

● Office graphic reproduction —Growth i n the use of intel -Iigent copier/printers will encourage more in-house offsetprinting. Timeframe: currently taking place; trend is ex-pected to continue.

Duplexing and reduction capabilities, both of which oper-ate to conserve paper, will become common features ofoffice copiers, including those positioned at the low endof the price scale. Timeframe: currently taking place; trendis expected to continue.

Converting papers:●

●

●

✎

Envelopes- Expanded use of electronic mail and voice-message systems may hold down the number of envelopesused by businesses and individuals. (Voice-message sys-tems are not expected to come into widespread use before1985.)Business forms—An increased proportion of businessforms will be produced in-house using intelligent copier-printers. Electronic storage and microforms will continueto displace paper forms in selected applications.Stationery and tab/et—A modest, negative impact fromelectronic mail, electronic pads, and voice-message sys-tems appears possible. Timeframe: beyond 1985.

Magazine publishing: Modest, negative impact possible fromhome video information. The future development of a full-page portable display for reading electronically stored in-formation could also impact paper consumption by maga-zines. (The advent of portable displays is not anticipateduntil the 1985-95 timeframe, or beyond.)

Other periodical publishing: Home video information mayhold down paper consumption for catalogs and direc-tories. The future use of videodiscs as a storage mediumfor reference materials may have a negative influence onpaper consumption for catalogs and directories. Time-frame: beyond 1985.

Book publishing: Possible use of home and office videodiscsto store large quantities of infrequently examined infor-mation could limit future demand for reference bookssuch as encyclopedias. Interactive videotex may Iikewisehave a negative influence on the demand for referencebooks. Timeframe: beyond 1985.

As noted above, next to magazines, the advent of a por-table, full-page display possessing adequate image qualityfor prolonged periods of reading may lead to reductionsi n the demand for paper-based, printed materials, includ-ing books. Timeframe: 1985-95, or beyond.

Computerized printers reduce the need for special labelsin certain applications.

Newspaper publishing: Home video information may drawclassified advertising and financial listings away fromnewspapers. It may also compete with newspapers bybecoming an efficient transmitter of time-critical news in-formation. Timeframe: beyond 1985.

Advent of compact display could also have repercus-sions on newsprint consumption. Timeframe: 1985-95,or beyond.

SOURCE American Paper Institute, Information Technology and Paper Demand (New York, API, 1981), pp 10-11

tronic media affect newspaper advertising astelevision has, by 1995 they could displace800,000 metric tons (tonnes) of newsprint an-nually (15 percent of current U.S. production),

In the short term, demand for writing andprinting paper seems to have increased withthe proliferation of word processors and officecopiers, which enable fast and inexpensivecopies of texts and graphics to be made, Al-though this phenomenon is considered bysome industry analysts to be temporary, othersforecast that paper will continue to dominateoffice communications, magazines, and news-papers.39 However, both International BusinessMachines (IBM) and American Telephone andTelegraph (AT&T) have stepped up activitiesin the field of information storage and transmit-

SQFree~ rn~ n, op. (: it., P. Go.

tal, and some analysts consider their entry intothe market as the harbinger of rapid progressand expansion in electronic communications. M

With 30 percent of U.S. paper production be-ing used for storage and transmission of infor-mation, the short-term trend in increased pa-per usage as a result of electronic officeequipment is expected by some industry ana-lysts to give way to sharp decreases in paperuse during the next 20 years .*1

The future impact of electronic media on pa-per demand may depend on its effects on theattitudes of a generation of children accus-

40(;. 11 rown, “Tomorrow in the Pulp and Paper Industry: AnOutsider’s v’iew, ” speech to 1982 Annual Employee RegulationsConferen(;e of the American Paper Institute and Fiber Box Asso-ciation, St. Louis, Me., ]an. 27, 1982 (New York: Kidder Peabody’and Co., Inc., 1982), p. 4.

41 ibid.

Ch. Ill—Pulp, Paper, and Fiber Products . 79

tomed to the partial substitution of electronicsfor paper. While many older people, not so ac-customed, find acceptance of nonprinted me-dia difficult, the present school-age generation,who use nonprinted communications through-out their educational careers, will accept elec-tronic communications for business and homeuse more readily. In addition, although current

technology limits the use of electronic commu-nication to desktop consoles and large comput-er and wordprocessing installations, the devel-opment of handheld portable devices withreadable screens—and microelectronic proces-sors capable of storing entire books and mag-azines—could have a significant impact on thesubstitution of electronic media for print.

Pulp, Paper, and Cellulose Fiber Manufacturing

Paper was supposedly invented in 105 A.D.by Ts’ai Lun, a member of the Chinese imperialcourt. 42 Ts’ai Lun’s method for papermakinginvolved soaking tree bark, hemp, rags andother cellulosic materials in water to softenthem and then beating the softened materialuntil the fibers separated and swelled. He dis-persed the fibers in a wet suspension andformed a thin sheet that was transferred to afelt cloth and pressed. The resulting web wasdried in the sun.

Paper is still made by essentially the sameprocess: 1) pulping, to separate and clean thefibers; 2) beating and refining the fibers; 3) di-luting, to form a thin fiber slurry, suspendedin solution; 4) forming a web of fibers on a thinscreen; 5) pressing the web to increase the den-sity of the material and remove excess liquid;6) drying to remove remaining moisture; and7) finishing, to provide a suitable surface forthe end use. The three methods for pulpingwood and other cellulose materials includechemical pulping, mechanical pulping, andsemichemical or chemimechanical pulping—acombination of the first two methods.

In mechanical pulping, wood chips from de-barked logs are ground, or are passed througha mill, and in some versions of the process aretreated with high-pressure steam (thermo-mechanical) to separate the individual fibers,which can then be formed into sheets of pa-per. Mechanically separated fibers contain lig-

4zF, F, Wa ngaa rd, WOOd: lfs Structure and properties ((] nl ~’er-sity Park, Pa.: Pennsylvania State Uni\’ersity, 1981), p. 335,

nin, which makes them remain stiff, bond poor-ly, and yellow with age.

Chemical pulping is done by cooking woodchips in acid, alkaline, or neutral salt solutionsunder pressure and high temperatures, whichbreaks down the wood structure and dissolvessome or most of the lignin and hemicellulosecontents. Delignification by chemicals causesthe individual fibers to become flexible and in-creases contact and binding among the fibersforming the paper mat, thus increasing thestrength of the paper. Semichemical and chem-imechanical pulping first breaks down thewood chemically, then by grinding.

The range of commercial pulping processescurrently used by the pulp and paper industryis shown in table 26. Nearly three-fourths ofthe wood pulp is produced by the kraft proc-ess (fig. 22).

Mechanical Pulping

Commercial Mechanical Pulping Technologies

There are four basic mechanical pulpingprocesses: 1) stone groundwood pulping, 2) re-finer mechanical pulping, 3) thermomechani-cal pulping, and 4) the recycling of paper. Flowdiagrams of the three mechanical pulping proc-esses are shown in figure 23. Mechanical pulp-ing is generally used with softwoods becauseof the added strength imparted by the long fi-ber length of softwood species. Mechanicalpulps are used principally to manufacturenewsprint, printing papers, and tissues that donot require high-strength paper. Secondary

80 • Wood Use: U.S. Competitiveness and Technology

Table 26.—Major Commercial Wood-Pulping Methods, Grades of Pulp, and End-Products

Pulp grades

Chemical pulps:Sulfite pulp . . . .

Kraft sulfate pulp

Dissolving pulp

Percent yield perWood type dry weight of wood End-products, utilizing grade

. . . . . . . . . . . . . . Softwoods and hardwoods 53-56 bIc

45-50 a’d

. . . . . . . . . . . . . Softwoods and hardwoods 40-50a

52-53b

. . . . . . . . . . . .Softwood 33-35

Semichemical pulps:Cold-caustic process . . . . . . . . . . . Hardwoods and softwoods 80-95

Neutral sulfite process . . . . . . . . Hardwoods 70-80

Mechanical pulps:Stone groundwoode . . . . . . . . . . . . Softwoods 95Refiner mechanical (RMP)e . . . . . . Softwoods 95

Thermomechanical (TMP)e . . . . . .Softwoods 95

Fine and printing papers

Bleached—printing and writingpapers, paperboard. Unbleached—heavy packaging papers,paperboard

Viscose rayon, cellophane, acetatefibers, and film

Newsprint and groundwood printingpapers

Newsprint and groundwood printingpapers

Corrugating mediumNewsprint and groundwood printing

papersNewsprint and groundwood printing

papers—aBleached pulps made from softwoodsbun bleached pulps made from softwoods.

cUnbleached pulps made from hardwoodsdBleached pUIpS made from hardwoods‘For paper and board

SOURCE George H Boyd Ill and Chad E Brown, Paper /r?dusfry. Ouf/ook for Market Pu/p (New York Kidder, Peabody & Co , 1981), p 5

Figure 22.— Proportions of Woodpulp Producedby Commercial Pulping ProcessesUnbleached kraft

380/o

Sulfite40/0

\ - - ’

Ground wood90/0

uses include wallpaper and paperboard. Re-cycled pulp is used mainly for the manufactureof folding boxboard (grayboard), tissue, cor-rugated board, and newsprint.

In the stone groundwood (SG) process, de-barked short logs (roundwood) are fed wholeinto grinders. The abrasion of the grinding

wheel against the wood physically separatesthe wood fibers. The grinding process usuallyis automatic and continuous, although some-times it is semicontinuous, Refiner mechani-cal pulping (RMP) uses chips in lieu of round-wood and produces paper with higher strengththan conventional groundwood because of lessdamage to the fibers in the pulping process, Awider range of species, including hardwoods,can be processed by the refiner pulpingprocess.

The most advanced commercial mechanicalpulping system is the thermomechanical proc-ess (TMP), which was developed as a modifica-tion of the RMP process. In TMP, wood chipsare steamed for several minutes under pres-sures ranging from 4 to 45 psi and subsequentlyrefined in one or two stages.

Recycled pulp is manufactured from waste-paper, which is processed into paper stock forfurther use in making paper. A small propor-tion of the paper stock (5 to 10 percent) is de-inked, usually with caustic, soda-based chem-icals. Most recycled paper, however, is pulpedwithout de-inking. Pulping is accomplishedthrough violent agitation and shearing action


Figure 24.—Wood and Energy Flows in Mechanical Pulping Mills in ConjunctionWith Recycling

twaste paper

I

I

I

I 400 Ibs , ~

310 Ibswastepaper I

II

of kraft pulp to improve its wet strength andprocessing on the paper machine. While paperusing TMP consumes 11 to 13 percent lesschemical pulp than ordinary newsprint, im-proved materials efficiency is gained at the ex-pense of higher energy consumption. When thecost of energy is considered as well as the costof wood, TMP is actually more costly than SG.Pulp yields from all the mechanical pulping

processes typically are near 95 percent recov-ery, which is a higher yield per unit of woodthan with the chemical pulping methods. Theprincipal variables that influence the choice ofmechanical pulping methods are: 1) furnish(raw material) requirements or wood species,2) pulp strength, 3) expected gross energy con-sumption, and 4) expected net energy con-sumption.

Ch. III—Pulp, Paper, and Fiber Products ● 8 3

The process variables that affect the qualityof mechanically produced pulp are listed intable 27. Increases in paper strength are gainedby increases in energy consumption, but bright-ness and opacity, qualities that affect the useof paper for printing, are largely independentof the pulping process. Recycling can effective-ly reduce the consumption of both wood rawmaterial and energy when used in conjunctionwith other mechanical pulping processes.However, it does so at the sacrifice of some pa-per strength.

Improvements in Mechanical Pulping

Technical improvements in mechanical pulp-ing have largely been directed at reducingenergy consumption and improving the qualityof mechanical pulps. Pulp yield is approachingthe practical upper limit, since all of the ligninand most of the hemicelluloses remain in thefiber, and fiber recovery from mechanical pulp-ing is frequently twice as high as that fromcompetitive chemical pulping. By reducingenergy costs, mechanical pulping has remainedcost competitive, and improvements in paperquality have enabled mechanical pulps to dis-place some of the more costly, higher qualitypulps produced by chemical processes. Asnoted in table 27, although improvements inquality result in some increases in the con-sumption of energy, the higher quality pulpproduced more than offsets the higher costs ofenergy.

Three major developments in mechanicalpulping technologies show promise for improv-ing pulp quality and/or reducing energy con-sumption: 1) pressurized groundwood (PGW)pulping, 2) chemithermomechanical pulping(CTMP), and 3) hardwood chemimechanicalpulping (CMP). Each of these new processeshas reached some stage of commercialization.A fourth major development is waste-heat re-covery.

PRESSURIZED GROUNDWOOD PULPING

In PGW pulping, debarked logs are fed to thegrinding wheel through a heated, pressurizedchamber. The heat and pressure help separatethe fibers, breaking down fewer fibers in thegrinding process and improving pulp quality.The longer fibers give the end product a highertear index than paper made from SG, but it isslightly inferior to that of TMP. The tear resist-ance for PGW pulp is 5.6, compared with 3.9for SG and 7.1 for TMP (table 27), The tensileindex for PGW pulp (35) also lies between thatfor SG pulp (32) and TMP (37). In addition toimproved strength, PGW promises some reduc-tion in energy consumption. It is estimated thatthe energy requirement may be reduced by 40percent from that required for the thermome-chanical process, or from 1,833 to 2,417 kWh/ton of pulp to approximately 1,100 to 1,450kWh/ton. 43

43 C;, \V. E\ans, “Pressured Process for Grounciwoo[] Pr{jdl]( -tion Making Health~’ Progress, “ })ujp a~]d }~a[}(~r, [’()] 54. 1980,

pp. 76-78.

Table 27.—Summary of Process Variables for Mechanical Pulping (based on the production of 1 ton of ovendry pulp)

Process

Ground wood Refiner mechanical ThermomechanicalVariable pulping pulping pulping Recycle

F u r n i s h t y p e . , Debarked logs Residual chips, Residual chips, Waste papersawdust sawdust

Furnish requirements . . . . . 2,100 lb 2,100 lb 2,100 lb 2,200 lbEnergy requirements (kWh/ton) . 1,340-1,790 1,800-2,400 1,800-2,000 360Strength:

Burst . . . . . . . . . . . . . . . 1.4 1.8 2,0Tear . . . . . . . . . . . . . . . . . . . . 3.9 5,7 7.1Tensile, . . . . . . . 32.0 35.0 37.0

Other:Brightness . 60.0 57.0 57.0Opacity . ., . 95.0 95.0 94.0


By 1980, five mills worldwide had installedPGW systems. Fifteen more plants have beenordered, including four to be located in theUnited States. Some industry analysts considerPGW technology to have significant potentialfor reducing mechanical pulping energy re-quirements and for displacing some high-qual-ity chemical pulps in the manufacture of news-print and other printing papers.

CHEMITHERMOMECHANlCAL PULPING

CTMP involves treating softwood chips withmild sulfite solutions prior to pulping. This“sulfonation” treatment results in paper withhigher tear indices than do TMP, RMP, or SGpulping processes.44 Energy consumption forCTMP may range from 1,360 kWh/ton to 2,000kWh/ton, depending on the strength of thesulfite solution. Thus, energy consumption ofCTMP lies within the range of SG pulping, isless than that required for RMP or TMP, andresults in a higher quality paper. Pulp yieldsdecrease slightly to between 85 and 95 percentwith CTMP, but these yields are still large com-pared to chemical pulping and to mechanicalchemical pulp blends. Some TMP pulpmillshave begun to add sulfite chemicals in theiroperations to improve pulp quality and reduceenergy consumption.

HARDWOOD CHEMIMECHANICAL PULPING

Mechanical methods for producing pulpfrom underutilized hardwood species involvepretreating hardwood chips with hydrogenperoxide or sodium hydroxide and processingthem like RMP. Both poplar [softwood) and redoak (hardwood) have been pulped successfullyby these techniques. However, fiber recoveriesare lower for hardwood CMP than for soft-wood CMP. Pulp recoveries of 80 to 85 percenthave been reported for poplar, 90 to 95 percentfor red oak.

Energy consumption for CMP ranges from500 to 1,500 kWh/ton using hydrogen perox-ide for chemical pretreatment and 700 to 1,100

.44~ Atack, et ~]., “Sulphite Chemimechanical Refiner Pulp-Another Option for Newsprint, ” Pulp and Paper, vol. 54, 1980,Pp. 70-72.

kWh/ton using sodium hydroxide.45 HardwoodCMP consumes significantly less energy thando either SG or other chemimechanical hard-wood pulping technologies.

Pulp and paper technologists expect hard-wood CMP to expand significantly during thenext 10 to 25 years because of the large volumesof inexpensive hardwood available, a phenom-enon that could have a profound impact on theutilization of presently underutilized speciessuch as poplars, red alder, and American syc-amore that are abundant throughout the East-ern United States. Pulp produced by hardwoodCMP can be used to produce newsprint andprinting papers. Two small U.S. mills, whichrange in capacity from 200 to 250 tons of pulpper day, have already installed CMP systemsto process hardwood species.

WASTE HEAT RECOVERY SYSTEMS

Mechanical pulping systems create a largeamount of frictional heat during the grindingand refining processes. Heat recovery systemsthat enable use of waste heat (for drying pa-per, space heating, and water treating) are im-portant to the reduction of energy costs in thepulping process. Such systems are particularlyimportant in TMP, which requires large quan-tities of mechanical energy and produces high-quality heat (i.e., high heat under temperatureand adequate pressure) .46 Because of the highertemperature of waste heat from TMP proc-esses, a higher percentage of usable waste heatcan be recovered from TMP than from conven-tional groundwood pulping,

Heat recovery technologies currently recap-ture 3 million to 5 million Btu/ton of pulp pro-duced.” For mills consuming 1,800 to 2,400kWh/ton, 95 percent efficiency in heat recoverywould represent a total of 5.8 million to 7.8 mil-

45J, D. Sinkey, ‘lCMP and C’I’MP-A Review,” paper presentedat Forest Products Resear[;h Society Conference, St. Paul, Minn.,1981.

4EP, J. Walker and E, J. 13atsis, “Heat Recovery From TMP Oper-ations Results in linergy Consert’ation, Pulp and Paper, vol.52, 1978, pp. 146-148.

‘T’rhe Fossj) ~’nerg~, ~’onser~,atjon Potential Associated W’iihProducing Wood Pr’oducts From Managed Stands (Bellekwe,Wash.: Envirosphere Co., 1981).

Ch. Ill—Pulp. Paper, and Fiber Products . 85

lion Btu.48 With current technology, the indus-try captures 50 to 65 percent of the theoreti-cally recoverable waste heat, Widespreadadoption of these efficient systems has not yetoccurred because of the problems of retrofit-ting and high capital costs.

Future Prospects for Mechanical Pulping

The three major new mechanical pulping tech-nologies—PGW pulping, CTMP, and CMP—have improved pulp quality and reduced en-ergy consumption compared with convention-al groundwood processes. The resulting higherquality mechanical pulps will displace the kraftpulps that are currently mixed with mechani-cal pulps to improve paper strength. For ex-ample, the shift from SG pulping to TMP dis-placed 300 pounds of kraft pulp per ton ofnewsprint. Use of the new technologies willfurther reduce the amount of kraft pulp re-quired in newsprint and printing papers, re-ducing the demand for softwood timber be-cause the pulp yield from these processes isnearly twice that of kraft processes.

The configuration of mechanical pulpmillsfor newsprint manufacturing will likely changesignificantly during the next 10 to 20 years.By employing CMP and CTMP technologies,using a higher percentage of hardwood as rawmaterial, and installing highly efficient heatrecovery systems (85 percent recovery), the me-chanical pulpmill of the future could reduceits heat requirements by 1.0 million Btu [300kWh/ton of heat) and reduce electrical energyconsumption by 97o kWh/ton of newsprintfrom that currently required by TMP mills.Savings of this magnitude of purchased elec-tric power is equivalent to a savings of 11 mil-lion Btu of heat input at the powerplant. In ad-dition, 3.5 million Btu of usable heat could berecovered, offsetting over 50 percent of thatcurrently required in the pulp and papermak-ing process.

Further improvements in energy efficiencyand wood utilization could result if a recyclepulpmill were integrated with either SG orTMP pulpmills (fig. 25). The practical upper

limit of recycled fiber in the pulp mix is esti-mated to be about 40 percent. A small propor-tion of kraft pulp is required in the mix tostrengthen the newsprint if larger proportionsof recycled pulp are used.49 The major gainsin energy efficiency between a wholly round-wood C M P or CT M P mill and one integratedwith a recycle pulpmill are in reduced electri-cal-energy consumption. Reductions in energyconsumption of between 179 and 358 kWh/tonof pulp may be achieved by recycling, so Proc-ess heat requirements remain approximatelythe same when recycling is used, but theamount of recoverable waste heat is decreasedfrom 3.5 million to 2,2 million Btu.

Substantial technical improvements are pos-sible in mechanical pulping processes withinthe next 20 years, providing that economic in-centives exist and capital formation is possible.

Chemical Pulping

Commercial Chemical Pulping Technologies

Chemical pulping processes involve treatingwood chips with chemicals to remove the lig-nin and hemicellulose, thus separating anddelignifying the fibers, Delignification gives thefibers greater flexibility, resulting in a substan-tially stronger sheet of paper—because of great-er contact between the fibers in the finishedsheet—than can be manufactured from fiberswith lignin produced by mechanical pulping.

Two major chemical pulping technologiesare currently in use: 1) kraft (sulfate) pulpingand 2) sulfite pulping. The kraft process dom-inates the pulp and paper industry, account-ing for over 75 percent of all pulp producedfor paper and paperboard in 1979.51 Otherchemical pulping processes, such as acid sul-fite pulping, bisulfite pulping, and neutral sul-fite semichemical pulping account for approx-imately 3 percent (the remainder was producedby mechanical pulping), Paper made from pulp


IIII

III

I Oil

I

I

Coal I

I

I

II

I

t 1

I

iPaper (1 D ton)

IIIIIIIII

I

II

III

IIIIIIIII

IIII


produced by the kraft process accounts formost of the bleached boxboard and linerboardused by the packaging industry (which con-sumes 58 percent of the paper in the UnitedStates).

In addition, bleached softwood kraft pulpsoften are mixed with mechanical pulps to addstrength to newsprint and printing papers.Bleached hardwood kraft pulps are added tobleached softwood pulp to improve printabilityfor specialty paper products like magazinestock and coated papers.

KRAFT (SULFATE) PULPING

The kraft process involves treating woodchips and sawdust with a sodium sulfide andsodium hydroxide solution. The highly alkalinechemical mixture is cooked in a digester for1 to 3 hours at temperatures ranging from 320°to 3500 F (fig. 25). The complete pulp and pa-per making process is shown in figure 26.

Fiber recovery from the kraft pulping proc-ess is largely a function of the wood speciesused, the amount of chemicals used, the timeand temperature of cooking, the degree ofbleaching, and the paper strength required.Generally, kraft pulp recoveries from soft-woods are approximately 47 percent for un-bleached pulp and 44 percent for bleached. s’Hardwood recoveries range from 50 to 52 per-cent for unbleached kraft pulp and 45 to 50 per-cent for bleached.

Energy is used in a mill in different forms(as chemical heat of reaction, as thermal ener-gy, and as electrical energy), and these typicallyare expressed in different units (Btu for ther-mal and for heat of reaction in fuel combus-tion, and kWh for electricity). While the unitsmay be converted simply (i.e., 1 kwh = 3,412Btu), the actual forms of energy may not be con-verted without loss of energy available for do-ing useful work. Thus, in a typical powerplant,it takes 10,000 Btu of heat input to produce 1kWh of electricity (in contrast to the unit con-version above), and two-thirds of the input is

szp, J Hu~~ey, Comparison of Mills Energy Balance: Effects

of Conventional Hydropyrolysis and Dry Pyrolysis Recovery Sys-tems (Appleton, Wis.: Institute of Paper Chemistry, 1978).

lost as exhaust. There are, then, two ways tocompare a mill’s energy uses: 1) simple unitconversions, representing all uses in a commonunit; or 2) representing all uses in terms of theheat values of their original forms, while recog-nizing energy conversion losses.

The different conclusions reached by theseapproaches is illustrated by the following: thefirst method gives rise to the conclusion thatself-generation in today’s typical kraft papermill provides about 50 percent of the mill’s en-ergy needs, while the second method (table 28)shows that 82 percent of the primary fuel sup-plying the total energy needs of a typical kraftmill is self-generated. The first method relatesbetter to concerns for fossil-fuel avoidance,while the second helps relate the fuel value ofwood-process residuals to other potential uses.Of the two approaches, the latter is the moreuseful for assessing process efficiency.

Energy consumption is a major cost in themanufacture of kraft pulp and paper. The com-bined process requires approximately 30 mil-lion Btu of primary fuel per ton of bleachedkraft paper (table 29). This energy value in-cludes fossil fuel burned at an outside power-plant to provide purchased electricity as wellas the thermal energy derived from the woodresource. Approximately 78 percent of the en-ergy demand is for thermal energy used in theplant, the major portion of which is used forpaper making and self-generation of electricityrather than in the pulping process. While thecombined kraft pulp and paper making proc-ess requires approximately 1,050 kWh/ton ofelectricity, mostly for drive motors, all but 101kWh generally is produced internally throughcogeneration (table 29). Burning waste liquorsand bark provides 82 percent of a mill’s pri-mary energy needs.

The kraft process is suitable for pulping bothsoftwoods and hardwoods. Wood chips, saw-dust, and wood residues from sawmills and ve-neer mills can be used as furnish, Over 35 per-cent of the total wood supplied for kraft paperare wood residues. In the Pacific Northwest,nearly 90 percent of the wood originates fromsawmill or veneer mill residues. Whole treechips, including bark and branches, currently

are used in limited quantities, although theirproportion of the total furnish is increasing. Be-cause of the density, extractive content, andchemical nature of these materials, increasesin their use may cause the pulping liquors(chemicals) to react more slowly, resulting ina need for longer digestion periods and in-creased energy expenditures.

SULFITE PULPING

The four fundamental sulfite pulping proc-esses currently in commercial use are: 1) acidsulfite, 2) bisulfite, 3) neutral sulfite, and 4) al-kaline sulfite. The major differences betweenthe sulfite processes are the levels of acidityand alkalinity of the sulfite chemical solutionsused to break down the wood and remove thelignins. The cooking liquor consists of a saltbase—generally calcium, magnesium, sodium

or ammonium—and sulfuric acid. Sulfite proc-esses are suitable only for species with low ex-tractive contents, i.e., those low in tannins,polyphenols, pigments, resins, fats, and thelike, because of the interference of these sub-stances with the sulfur pulping process. Al-though calcium is the cheapest base available,it forms insoluble compounds that cannot bereclaimed economically or disposed of easily.Thus, calcium-based pulping is seldom used.Because magnesium- and sodium-based chem-icals are recoverable, and ammonium-basedchemicals can be burned without harmful envi-ronmental effects, they are the most frequentlyused.

Sodium-based sulfite pulping can consist ofmultistage cooking, successive stages of whichdiffer in acidity. Because one stage optimizeschemical liquor penetration and the other the


Table 28.—Energy Demand Per Ton of Kraft Paper

Thermal:Process:

Digester. ... .Bleach plant .Paper machineEvaporation. .,Liquid heatingOther . . . . . . . .

Subtotal ... . .Lime kiln . .

Total . ... . .

Electric:Self -generated:

Energy demands

Million Btu

. . . . . . . . . . . . . 3.8

. . . . . . . . . . . . . . 2.4

. . . . . . . . . . 6.8

. . . . . . . . . . . . . 3.0

. . . . 2.9

. . . . . . . . . . . . 2,5

. . . . . . . . . . . . 21,4

. . . . . . . . . . . . . . 2,0

. . . 23.4

. . . .Fuel-value material recovered inplant and burned for electricity 5.7b

Purchased f rom outs ide: . . . . . .Fuel used by outside powerplantto produce electricity . . . . . . . . 1 .0c

Totals:Total electricity . ... . ...Total fossil fuel consumed . . . . . . 30.1—

aHurley, P J

kWh

949a

101 a

1,050

blncremental heat ra[e tO generate electricity In plant 6000 BtulkWh

cAssumes out SI de electrlc PI ant IS fess! l-fueled at 10,000 BtulkWh

SOURCES J J Watkins and W S Adams, “The St Regls Hydrolysis Processas an Approach to Energy Conservation In the Pu 1P & Paper Industry, ”Proceed~ngs of TAPP/ ’78 Engfr?eenrrg Corrference Book ///P J Hurley, Corrrpar/son of Mi//s Energy Rdar?ce Effects of Convenf/ona/ Hydropyro/ys/s and Dry Pyrolysls Recovery Sys(erns (Appleton,WIS Institute of Paper Chemistry, 1978)

removal of lignin, more lignin may be removedwith less fiber degradation, so that fiber yieldsare higher, fibers are stronger, and a widerrange of wood species may be used. Neutralsulfite pulping, using sodium and ammoniumbases, recovers the largest proportion of fiber(75 to 90 percent) of all the sulfite pulpingmethods.

Improvements in Chemical Pulping

Two kinds of improvements have been madein chemical pulping technologies: 1) better effi-

ciency of current processes and 2) developmentof new pulping technologies that depart fromthe conventional commercial processes. Thegreatest potential for dramatically improvingpulp and paper manufacturing lies in new tech-nologies. Such innovations could enable theuse of large quantities of currently underuti-lized hardwood species and may even haveprospects for developing superior new papersfor future specialized uses. At the same time,new concepts in energy use and cogenerationcould achieve new levels of energy efficiencies.Among the most promising new pulping andpapermaking processes are: 1) press-dried pa-per, 2) green liquor pulping, 3] autocausticiz-ing, and 4) pyrolytic recovery of chemicals inspent pulping liquor. These developing tech-nologies are not yet commercially available.

PROCESS IMPROVEMENTS

Major efforts in process improvements, ormeans in which the efficiency of existing com-mercial processes is improved, have centeredon increasing fiber recovery and energy effi-ciency. Most such efforts have focused on thekraft process, which produces 90 percent of allchemical pulps manufactured. Greatest empha-sis has been placed on reducing energy con-sumption because it is the largest cost factor.

Anthraquinone (AQ) recently has been testedas a catalyst in kraft pulping. When added insmall quantities to the cooking liquor, AQspeeds up the pulping process and can improvefiber recovery by as much as 2 to 4 percent.Although the percentage increase in yield mayseem small, the increases in absolute yield areconsidered substantial because of the verylarge volumes involved. AQ pulping was de-veloped by Canadian Industries, Inc., and is

Table 29.—Energy Consequences of Pyrolytic Recovery (basis: 1 ton pulp)

Recovery methodEnergy required Conventional hydropyrolysis Dry pyrolysis

Process yield (percent ovendried) . . . . . . . . . . . . 47.5 48.75 47.5Electricity (kWh):

Internally generated . . . . . . . . . . . . . . . . . . . . . . . . . 949 850 812Purchased . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 256 258

Inplant fossil fuel (thousand Btu) ... . . . . . . . . . . . . . . . 10,411 5,458 6,296Inplant fossil-fuel savings (percent). . . . . . . . . . . . . . . . . . . . 48 0/0 40 ”/0

Paper Chemistry 1978)


used commercially in both Japan and theUnited States. Its potential broad-scale applica-tion in the United States, however, maybe lim-ited by its cost and the lack of technology torecover the used AQ.53 The U.S. Food and DrugAdministration (FDA) recently has approvedAQ for use in paper packing for food, open-ing new market potentials for AQ pulp.

The industry’s goal is for the kraft pulpingprocess to become as energy self-sufficient aspossible. Substantial gains in energy efficiencyare expected within the next 20 years, but itis not known whether total self-sufficiency isattainable. Kraft mills may approach self-suf-ficiency if some modifications are made; forexample: 1) the temperatures in boilers thatburn wood residues and black (lignin) liquorcan be reduced (primarily by adding more ef-ficient heat exchangers for heat recovery, and2) lime kilns maybe fueled with dried sawdustwithout seriously contaminating the calcinedlime used for making the pulping liquor. Thelatter has been demonstrated successfully inSweden. 54 These system modifications are ex-pensive and may increase the operating costsof a plant. Their adoption will depend on thefuture costs of energy and the availability ofcapital.

GREEN LIQUOR PULPING AND AUTOCAUSTICIZATION

Economy in chemical pulping depends on ef-fective recovery of chemicals from the usedcooking liquor. Upon interaction with wood inthe cooking process, the “white liquor, ” thatis, the original sodium sulfide and sodium hy-droxide solution, becomes “black liquor,” richin lignin salts and other organics removed fromthe wood in the pulping process. The black liq-uor is pumped to evaporators that remove thewater and concentrate the remaining salts andorganic solids. The resulting viscous solutionis burned in a recovery furnace to remove theorganic residues (fig. 26).

The remaining salts—mostly sulfides and car-bonates of soda—form a molten stream re-

ferred to as “smelt” and are recombined withwater to form “green liquor. ” The sodium car-bonates in the green liquor normally are con-verted into hydroxides for reuse by the addi-tion of calcium hydroxide in a process referredto as “causticizing.”

Pulping of hardwoods and softwoods usinggreen liquor, which eliminates the causticiz-ing process, is now an accepted commercialtechnology for producing semichemical pulps.In this process, disodium borate is used insteadof sodium hydroxide in the original white liq-uor, and the liquor produced by dissolving thesmelt can be reused directly in the digester. Inthis way, the entire regeneration loop, includ-ing the lime kiln, is removed. As much as 18percent of the fossil energy required for pulp-ing can be eliminated by autocausticization.Elimination of the lime kiln not only reducesenergy consumption, but reduces capital costsby $35/annual ton of capacity and operatingcosts by $3/ton. 55 Industry experts give auto-causticizing a high probability of commercialacceptance.

PYROLYTIC RECOVERYTechnology for pyrolytic recovery of black

liquor has been developed in two processes: 1)a hydropyrolysis method developed by the St.Regis Paper Co., and 2) a dry pyrolysis methoddeveloped by Weyerhauser Corp. Pyrolytic re-covery consists of applying heat in the absenceof oxygen (anaerobic combustion) to decom-pose the organic compounds in the black liq-uor. These new spent-liquor recovery tech-niques, designed to extract energy from thespent liquor while retaining the chemicals forreuse, are more energy efficient than are cur-rent processes. They are important because re-generation of the pulping chemicals requiresa large share of the energy used in the pulpingprocess.

Hydropyrolysis technology currently is be-ing evaluated on a pilot basis in St, Regis’ Pen-sacola, Fla., mill. The process shows potential

53Hub~r, op. cit., P. 85.WK. Lappe, “Advanced Drying Process is Key to Burning Peat,

Wood Byproducts, ” Energy Systems Guidebook (New York:McGraw-Hill, 1980).

‘5]. Jansen, “Pulping Processes Based on AutocausticizableBorate, ” The Delignification Methods of the Future (Helsinki,Finland: Europa Symposium, 1980).


for reducing the energy requirements for evap-orating weak black liquor, i.e., that recoveredin the initial washing stage, and for aiding inthe energy recovery process. It is estimated thatfossil-fuel energy required for generation ofprocess heat may be reduced by 50 percentwith the application of hydropyrolysis technol-og y. 56

St. Regis’ experience with its pilot plant in-dicates that application of hydropyrolysis tech-nology results in a tradeoff between purchasedfossil fuel and purchased electricity. Loweredheat requirements for liquor recovery result inless process steam; thus, the potential for co-generating electricity along with the steamneeded is limited. The results of these trade-offs are shown in table 29, where the data sug-gest that an in-mill fossil fuel savings of up to48 percent can be achieved with hydropyroly-sis and approximately 40 percent with drypyrolysis. However, considering the fossil fuelused to generate the purchased electricity, thenet fossil fuel savings are 28 percent and 20percent, respectively.

OTHER CHEMICAL PULPING TECHNOLOGIES

Attempts to develop alternative pulping tech-nologies that increase yields, energy efficiency,and pulp quality of the kraft process have ledto two new chemical pulping concepts thatshow some promise: 1) organosolv (alcoholysis)pulping and 2) oxygen pulping. Since both stillare under development, and neither hasreached the demonstration stage, they must beconsidered long-range (25 + years) prospectsfor commercial application,

Organosolv Pulping.-Organosolv pulping is atwo-stage process involving hydrolysis (decom-position of the wood by dilute acids or en-zymes) and the removal of lignin with an or-ganic solvent, usually a mixture of alcohol andwater. The still-experimental process is suitablefor both hardwoods and softwoods. Pulp recov-ery from organosolv pulping ranges between50 and 60 percent for hardwoods, and 40 and45 percent for softwoods. Typical hardwood-fiber recoveries compare favorably with those

from kraft pulping: approximately 50 percentfor red alder, sweetgum, and American syca-more, and 60 percent for cottonwood and trem-bling aspen.

Fibers produced by the organosolv processare weaker than those recovered by the kraftprocess, Thus, the papers produced fromorganosolv pulp are suitable for uses wherestrength is not the most important property,such as for printing papers, fluff pulps, anddissolving pulp,

Reaction temperatures are low—between320° and 370° F for hardwoods and 360° to3900 F for softwoods if acid catalysts are used.Little waste is produced by the process, andlow alcohols are recovered easily by distilla-tion, thus requiring relatively low capital in-vestment .57

Oxygen Pulping.—An extension of existing ox-ygen bleaching technologies, oxygen pulpingmay reduce or eliminate the need for bleachingplants in the paper mill. Oxygen pulping in-volves the introduction of gaseous oxygen intothe pulping liquor to stimulate oxidative frac-ture of the cellulose-lignin bonds. This proc-ess could save capital and operating costsbecause equipment costs are lowered, lessbleaching chemicals are used, and pollutioncontrol expense is cut by eliminating chlorinefrom the bleaching process.

The cost of oxygen pulping is largely a func-tion of the cost of oxygen. Oxygen productionrequires approximately 400 lbs of oxygen and54 kWh/ton of pulp produced (based on 1.2kWh/hundred cubic feet(H3),or0.135 kWh/lb.Several manufacturers currently are develop-ing plant equipment capable of applying oxy-gen pulping commercially.

PRESS DRYING PAPER

Press drying technology developed at FPLshows promise for both reducing the amountof energy required in the paper-making proc-ess and enabling the use of underutilized hard-

57N Sa ~, b.er, .$ta tcls of N~t%F Pulping Processes; Problems (i tl[]pe~s~ectjl,es (~fa~ison, Wis,: U.S. Forest P r o d u c t I.aborat(}r},1982], p. 10,


wood species. Press drying uses high-yieldhardwood or softwood kraft pulp to producelinerboard with strength superior to that ofconventional softwood kraft paper in every re-spect except tear strength (table 30). At thesame time, press drying can reduce the amountof energy used in the drying process by apply-ing pressure to the fiber (pulp) mat as it is dried.With conventional drying technology, pressureand heat are applied separately.

The superior strength of press-dried papercomes from the combined effects of heat andpressure, which force the fibers into closer con-tact and cause stronger bonds to be formed be-tween them. The heat and pressure also causenatural polymer flow and cross-linkages amongthe fibers as a result of the hemicellulose con-tained in the pulp. Paper produced from press-drying kraft red oak pulp has been shown tohave burst strength and tensile strength ap-proximately 13 percent higher, and compres-sion strength 50 percent better, than that ofconventionally dried pine kraft paper. Thelower tear strength of press-dried hardwoodpaper may limit its use for wrapping or sackpaper; however, its higher burst strength andtensile strength make it suitable for linerboard.

Estimates of the potential net energy savingsfrom using press-drying technology are about19 percent for the papermaking process, 58 Al-though a commercial-scale, press-dried paper-making machine has not been built yet, pressdrying may actually reduce equipment require-ments and capital investment in both the dry-ing section and the pulping process because

it can use unrefined pulp.59 The major limita-tion to press drying paper, which must be over-come before the technology can be appliedcommercially, is the low speed of the paper-making machine and the resulting slow pro-duction rate of the pilot-scale equipment usedat the FPL.

Dissolving Pulp Technologies

Dissolving pulp technologies are not pulpingtechnologies as such, but secondary processesthat produce nearly pure cellulose (alpha-cel-lulose) for conversion to rayon, plastics, andother chemicals. Pulps made by either the kraftor sulfite process are purified further chemi-cally to remove all hemicellulose and leave onlypure cellulose, which then can be transformedinto products like viscose rayon, cellophane,and acetate fibers and film. The largest singleuse for dissolving pulp is in the viscose rayonprocess, which accounts for over 99 percentof the world’s rayon production.

A variety of hardwood and softwood speciesis suitable for the production of dissolvingpulp, including pine, hemlock, spruce, oak,birch, and gum. Highly resinous wood, suchas Southern yellow pine, normally is not usedfor dissolving pulp because of the difficulty ofremoving extractives in the purification proc-ess. The highest grades of dissolving pulp arecalled cord, acetate, and nitrate pulps, whichapproach 98 percent pure cellulose; normalgrades of viscose rayon pulp contain somehemicellulose and maybe only 93 percent pure.Because of the need for nearly pure cellulose,

“v. Setterholm and Peter Ince, “The Press Drying Conceptfor Papermaking, ” Southern Lumberman, Dec. 15, 1980.

59P. J. Ince, “FPL Press Drying Process: Wood Savings in Liner-board Manufacture,” TAPPI, vol. 64, 1981, p, 109,

Table 30.—Strength Properties of Press-DriedHardwood Paper and Conventional Softwood Paper

Anticipated Present Conventionalstrength strength strengthwith oak with oak with pine

Burst strength (lb/in w)a . . . . . . . . . . . . . . . . 155 145 97Tensile strength (lb/in w) . . . . . . . . . . . . . . . 100 68 54Compression (lb/in w) . . . . . . . . . . . . . . . . . . 45 30 20aPounds per inch of width

SOURCE U S. Forest Products Laboratory, 1981

Ch. lIl—Pulp, Paper, and Fiber Products ● 9 3

pulping yields for the kraft and sulfite proc-esses are reduced to approximately 28 to 38percent, depending on the pulp purity desired.The low yield of high-quality, alpha-cellulosepulps makes them expensive to produce—en-ergy and pulpwood costs account for 50 to 60percent of the manufacturing costs.60

Total U.S. production of dissolving woodpulp was approximately 1.5 million short tonsin 1979 (23 percent of world production). Ap-proximately 61 percent of the dissolving pulpproduced was used for textile fibers; the re-mainder was used for the manufacture (in de-scending order) of chemicals and plastics, cel-lophane, cellulose nitrate (for propellants), andspecialty papers for use in industrial and auto-motive filters.

In addition to the viscose rayon process forthe production of fibers and cellophane (whichis made by the same viscose process but is ex-truded through a slot to form film rather thanthrough holes to form threads), cellulose maybe converted into acetate forms (acetyl esters)that can be manufactured into cellulose ace-tate, cellulose diacetate, and cellulose triacetatefor conversion into fibers. Cellulose nitratecontinues to be produced in significant quan-tities as an explosive and a propellant. Otherproducts manufactured from dissolving pulpinclude ice cream thickeners, detergents, car-bon fibers of high strength and stiffness, andgels used in hand lotions and food products.

Rayon Manufacture

Rayon, first made in 1881, is the oldest man-made synthetic fiber. The success of rayon inthe

●

●

market is due to several factors:

Cellulose continues to be the cheapestpolymer for fabrics.Rayon’s moisture absorption, capacity forabsorbing dyes, and ability to swell makesit suitable for clothing. Rayon also can beblended with other synthetic fibers, likenylon, to improve their moisture-absorbingqualities.

OOC, B. Metz, “Dissolving Pulps-The Future Economic Situ-ation, ” Proceedings of the 5th International Dis.~ol~in,g Pulp.sC o n f e r e n c e (~’ienna, Austria: Oct. 8-10, 1980).

● properties of the dissolving pulp can bevaried to produce pulps suited for specificend uses. For example, ITT Rayonier, aleading U.S. producer of dissolving pulps,offers 16 grades of pulp matched to theproperties of the rayon to be produced.

Rayon is made by dissolving cellulose xan-thate in alkali and spinning the fiber throughsmall pinhole jets into a sulfuric acid bath,which coagulates the fiber into final form. Ifthe same xanthate-viscose solution is forcedthrough a narrow slit, a cellophane film isformed.

Major developments in rayon technologyhave been aimed at:

improving the efficiency of rayon pro-duction;reducing energy requirements;controlling or eliminating environmentalpollutants generated by the viscose rayonprocess;developing more cottonlike rayons to sup-plement cotton production; anddeveloping a completely new system forconverting chemical cellulose to fiberby a nonviscose, environmentally sound,more efficient process using recoverablecellulose solvents. 6l

Major emphasis has been placed on devel-oping a rayon with a high wet-strength to rem-edy the shortcomings of conventional rayonand to compete with cotton more effectively.A number of new fibers outperform conven-tional rayon; they include Courtauld’s “Cor-val, ” a cross-linked fiber; American Viscose’s“Avril”; and Enka’s “Fiber 700. ”

Process developments within the rayon in-dustry seem to be moving toward automationand computer control. Experts foresee new,versatile rayons made by solvent-extrusionprocesses similar to those used for making ny-lon and polyester. These may lead to a futureo n e - s t e p process from pulp to viscose solut ion;

h o w e v e r , m a n y o f t h e c u r r e n t d e v e l o p m e n t s i n

t h i s a r e a a r e t r e a t e d a s p r o p r i e t a r y a n d a r e n o t

o p e n t o i n s p e c t i o n .

“G, Daul, “Rayon Revisited, ” Chemtech, Februarj 1981, p. 84.


The viscose process is one of the most ver-satile for manufacturing textile fibers. Modi-fication of the viscose manufacturing processeasily can accommodate stretching and orient-ing the fiber and building certain desired prop-erties into it. For example, it is known that theaddition of metallic salts, such as zinc andother modifiers, will delay the reformation torayon to allow time for spinning and manipu-lating the fiber. Formaldehyde also has beenfound to be an effective modifier for the pro-duction of super-strong fibers; however, envi-ronmental problems associated with it muststill be overcome. 62

Research to improve the strength and per-formance of rayon materials continues. Theseefforts include the search for new solvents foruse in the spinning (forming) process. One suchprocess that shows promise uses a special sol-vent (methyl-morpholine-N-oxide, MMNO) toorient the molecules in solution to form rayonwith high-strength cellulose fibers. Success ofthe MMNO process may depend on develop-ment of a solvent recovery system needed tomake the manufacturing process economicallycompetitive. 63 Some experts see the testing ofother new solvents leading to a major new sys-tem for manufacturing rayon. 64

Other Cellulosic Products

A number of otherfrom dissolving pulp.

‘Z1bid., l]. M.

products can be madeFor example, cellulose

L33R, N. A r m s t r o n g , C. C. McCorsky, and J. K. Varoa, ‘‘Spin-nable Solutions of Cellulose Dissolved in Amine Oxides, ” f%o-ctxxiings of the 5th International llissol~’ing PUII>S Conference[Vienna, Austria: oct. 8-10, 1980).

~411, I,. Hergert, R. B. Hammer, and A. F. Turbak, ‘‘New Meth-ods for Preparing Rayon, ’ Proceedings of the 4th InternationalDissol~ing Pulps Conference (Chicago, 111.: Sept. 28-30, 1977),

acetate is produced by steeping dissolving pulpor cotton liners in acetic acid to prepare fibersfor conversion to acetate, This same processmay be used to produce cellulose butyrate andcellulose propionate for the production ofplastics.

An acetate of slightly different chemicalform, cellulose triacetate, also can be madefrom dissolving pulp. Unlike rayon, it is water-repellent like nylon, orlon, and terylene. Itswater repellency is attributable to the degreeof acetylation of the fibers. It has good ther-mal properties and wear characteristics, andfrequently is used in fabric blends with nylon,wool, and rayon in women’s clothing.

Cellulose esters—acetate ester, acetate butyr-ate, and acetate propionate—are a family ofplastic materials derived from dissolving pulpthat can be formed, molded, and extruded bya variety of thermoplastic processes. Higherforms of these materials also maybe prepared;however, their high production costs restrictthem to highly specialized applications suchas cellulose acetate phthalate, which is used asa coating on pharmaceuticals. Cellulose esterpowders are used in fluidized-bed and electro-static coating processes, as well as in rotationalmolding processes. Modified cellulosic poly-mers are used in preparation of films, coatings,fibers, lacquers, and adhesives,

Finally, dissolving pulps also may be used toproduce a variety of chemical products, includ-ing methyl- and carboxymethyl-cellulose, thatare used as thickeners in latex paints and icecream; ethylcellulose, used as a thermoplasticmolding compound; and nitrocellulose, usedas a propellant/explosive.

chapter ii pulp, paper, and fiber products

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