Electron Processing Technology: A Promising Application for the

Viscose Industry

T. M. Stepanik, S. Rajagopal,D. Ewing, and R. Whitehouse

Atomic Energy of Canada LimitedWhiteshell Laboratories

Pinawa, ManitobaCanada R0E 1L0

Tel: 204 753 2311Fax: 204 753 8802

Presented at the 10th International Meeting on Radiation Processing11 - 16 May, 1997Anaheim Ca., USA

TO BE PUBLISHED IN THE 10TH IMRP CONFERENCE PROCEEDINGS INRADIATION PHYSICS AND CHEMISTRY JOURNAL

ELECTRON-PROCESSING TECHNOLOGY: A PROMISINGAPPLICATION FOR THE VISCOSE INDUSTRY

T. M. STEPANIK, S. RAJAGOPAL, D. EWING and R. WHITEHOUSEWhiteshell Laboratories, Atomic Energy of Canada Limited

Pinawa, Manitoba, Canada R0E 1L0

ABSTRACT

In marketing its IMPELA line of high-power, high-throughput industrial accelerators,Atomic Energy of Canada Limited (AECL) is working with viscose (rayon) companiesworld-wide to integrate electron-processing technology as part of the viscose manufacturingprocess. The viscose industry converts cellulose wood pulp into products such as staplefiber, filament, cord, film, packaging, and non-edible sausage casings. This multibillion dollarindustry is currently suffering from high production costs, and is facing increasingly stringentenvironmental regulations. The use of electron-treated pulp can significantly lowerproduction costs and can provide equally significant environmental benefits. This paperdescribes our current understanding of the benefits of using electron- treated pulp in thisprocess, and AECL’s efforts in developing this technology.

KEYWORDSAccelerators, irradiation, radiation, electron processing, viscose, rayon, cellulose, environmental

INTRODUCTION

After the pulp and paper industry, the viscose (rayon) industry is one of the largest processors ofcellulose. This industry converts cellulose wood pulp and cotton linters into filament, fiber, cord,casing, and film. These materials are used in clothing, fabrics, drapery, tires, packaging material(Cellophan), diapers, gauze, tea bags, non-edible sausage casings, garden hoses, sanding- and conveyorbelts, clutch pads, and automotive belts and hoses. In 1995, this multibillion dollar industry producedover 3 million tonnes of viscose materials, and showed moderate (2 to 3%) to major (5 to 10%) growthin production in all countries except Japan (Layman, 1996).

The viscose industry is faced with several problems, such as high chemical costs, and environmentalpollution. Electron-processing of cellulose prior to its use in making viscose can impact significantlyupon these problems. This paper describes the advantages of using electron-treated pulp in the viscoseprocess, and the efforts of AECL’s Biomass Group to promote this technology.

CELLULOSE STRUCTURE: EFFECT ON REACTIVITY

Cellulose is a linear polymer consisting of cellobiose repeating units (Figure 1A). Each unit contains 2anhydroglucose residues joined by a β-1,4-glycosidic bond (Nevell and Zeronian, 1985). The cellulosepolymer chain resembles a flat ribbon, with hydroxyl groups extending laterally from the edges, andhydrogen atoms oriented above and below the plane of the ribbon. This structure allows for extensiveinteractions between cellulose chains through hydrogen bonding between the hydroxyl groups, and Vander Waals interactions between the hydrogen atoms (Fengel and Wegener, 1989; Krässig, 1993;Fengel,1993). This results in a supramolecular structure (Figure 1B) composed of crystalline regions,where the chains are arranged in highly ordered three-dimensional lattices, and amorphous regions,where there is little or no order among the chains (Krässig, 1993; Fink et al., 1993).

In wood pulp, the amount of crystallinity varies between 60 and 70% (Fengel and Wegener, 1989).The amorphous regions are fully accessible to water and reagents, but the chain packing in thecrystalline regions is very dense, making these inaccessible to reagents and relatively unreactive. Thus,drastic conditions and high reagent concentrations are required for processing cellulose.

A

End View

CrystallineRegions

AmorphousRegion

CelluloseChains

CrystallineRegion

Top View

CelluloseChains

AmorphousRegion

B

O O

CH2OH

HO HO O O

CH2OH

HO

HO

O

4 5

6

32 1 4’

H

H

H

HH

H

H

H

H

H

Figure 1A: Cellobiose structure: Figure 1B; Supramolecular structure of cellulose.

THE VISCOSE PROCESS

Cellulose is first treated with high concentrations of alkali (18 to 20% w/w H2O) to produce alkalicellulose or AC (Cell-OH + NaOH → Cell-0- Na+ + H2O). Due to the inaccessible crystalline regionsin cellulose, a ratio of only about 1 NaOH is consumed per anhydroglucose residue (Treiber, 1985).After removing excess alkali, the AC is shredded, then incubated, or aged, in air for hours at 40°C orhigher. During this aging step, oxygen reacts with the AC causing cleavage of the cellulose chains,which is necessary for producing viscose with the right viscosity for spinning (Treiber, 1985). Highconcentrations (28% to 36%, w/w based on cellulose) of carbon disulfide, CS2, are then added to makea xanthate (Cell-0- Na+ + CS2 → Cell-O-C(=S)-S- Na+) containing approximately one ester group forevery 2 anhydroglucose residues. This amount of charged, bulky, xanthate groups is sufficient todisrupt the forces holding the chains together in the crystalline lattice formation, thereby promotingsolubilization in alkali. When the xanthate is dissolved in alkali, the resulting solution is called viscose.The viscose is stored for a short time, filtered, then spun in a bath containing high concentrations ofsulfuric acid, sodium sulfate, and zinc sulfate. During the spinning process, the acid neutralizes thealkali in the viscose and reverses the xanthation reaction. Solid cellulose and CS2 are regenerated, andH2S is produced as a side product (Treiber, 1985). Depending upon the type of spinning dye used, thecellulose is regenerated as fiber, cord, casing, or film. This material is then washed and subjected tofinishing treatments.

In most plants, the CS2 and H2S formed on spinning are released into the atmosphere. These chemicals,and the zinc used in the spin-bath, are toxic, and pose a major environmental problem (Treiber, 1990;Wolschner et al., 1995). Faced with increasingly strict environmental regulations, the industry isinvestigating methods for reducing these emissions.

IRRADIATED PULP: ADVANTAGES

Irradiation of cellulose causes cleavage of the cellulose chains and formation of more than 12 differentradiolytic products (Phillips, 1985; Nakamura et al., 1985). The chain cleavage produced by radiation isprecise, reproducible, and can substitute for the aging step in the conventional viscose process (Englundand Jones, 1957; Ueno et al., 1972; Laine et al., 1987). This can lead to superior process control,excellent viscose clarity, and increased throughput.

Unlike chemicals, radiation can easily penetrate the crystalline regions in cellulose and cause chemicaleffects that increase the accessibility of these regions to reagents (Horio et al., 1963; Fischer andGoldberg, 1987). The radiolytic products produced upon irradiation of cellulose differ significantly instructure from their anhydroglucose neighbors, and cannot participate as effectively in the bondingforces that exist in the crystalline lattices. This results in localized defects which weaken the latticestructures, improving their accessibility to reagents. Thus lower concentrations of chemicals such asCS2 and NaOH can be used to produce viscose (Fischer et al., 1980; Fisher et al., 1985; Fischer andGoldberg, 1987; Drozdovskii, 1991; Sokira and Belasheva, 1992; Stavtsov, 1996; Rajagopal et al.,1994; Rajagopal, 1995; Stepanik, 1995; Rajagopal and Stepanik, 1996; Stepanik et al., 1996;Soderlund, 1996). Reductions of 25 to 50% in CS2 and 16% or more in alkali are possible. With lessalkali used, less neutralizing acid is required during spinning. For a typical plant, the savings inchemical costs can amount to several million dollars US per year.

The use of irradiated pulp also has considerable environmental benefits. Less CS2 used means less CS2

and H2S are produced during the spinning process, and lesser amounts of these chemicals are releasedinto the atmosphere, reducing their effects upon the environment.

THE BIOMASS GROUP

The Biomass Group at AECL’s Whiteshell Laboratories is working with AECL Accelerators, a businessunit in AECL, to promote the use of IMPELA, AECL’s family of high-energy (10 MeV), high-powerlinear accelerators, in the viscose process. The Biomass Group has facilities for analyzing pulp beforeand after electron treatment, for producing viscose at the lab scale, and for assessing viscose qualityusing standard methods employed by the viscose industry. Collaborations with viscose producers havedemonstrated that significant reductions in CS2 , alkali, acid, and zinc can be achieved by using electron-treated pulp (Rajagopal et al., 1994; Rajagopal and Stepanik, 1996; Chincholkar et al., 1997).

More than 25 pulp- and viscose producers in 19 countries have been working with the Biomass Groupto optimize plant parameters (dose, amount of CS2, alkali, acid, and zinc, etc.) for using electron-treatedpulp. To date, 16 pulps have been evaluated, and processing conditions have been optimized for 3plants. Presently the Biomass Group is optimizing parameters for 4 more plants.

In 1995, the Biomass Group participated in a plant-scale trial involving over 100 tonnes of electron-treated pulp. The trial was held in Europe using pulp treated at Iotron Industries Inc., Vancouver,Canada. This trial was a complete success and led to a marketing trial in 1997 using several hundredtonnes of pulp which were treated at E-Beam Services Inc. in Cranbury, New Jersey, USA.

To market this technology, the Biomass Group and AECL Accelerators have partnered with ING. A.Maurer S.A., one of the 3 largest engineering firms that build new viscose plants and modify existingplants. This collaboration will accelerate the process for integrating accelerator technology into viscoseplants in the near future.

SUMMARY

Laboratory and plant-scale results have shown that use of irradiated pulp in the viscose process has thefollowing advantages: 1) significant reductions in CS2, alkali, acid, and zinc consumption resulting insavings in chemical costs of up to several million dollars US per year for a typical viscose plant; 2)considerable emission and effluent reductions for CS2, H2S, and zinc, leading to substantialenvironmental benefits; 3) significant savings in pollution abatement costs due to reduced effluent andemission loads; and 4) elimination or shortening of the cumbersome aging step resulting inimprovements in process operation and increased throughput.

The Biomass Group is working closely with AECL Accelerators and ING A. Maurer S.A. to promotethe use of electron accelerators in the viscose industry. This collaboration is unique in that the BiomassGroup provides a bridging function between an accelerator manufacturer, a viscose plant manufacturer,and a non-traditional end-user of accelerator technology. The Biomass Group is working with morethan 25 pulp and viscose companies to demonstrate the benefits of using electron-treated pulp. By theyear 2000, several producers will have conducted plant-scale trials and will be in the final stages ofimplementing electron-processing technology in their plants.

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