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Electron Processing Technology: A Promising Application for the Viscose Industry

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

Atomic Energy of Canada Limited Whiteshell Laboratories Pinawa, Manitoba Canada R0E 1L0

Tel: 204 753 2311 Fax: 204 753 8802

Presented at the 10th International Meeting on Radiation Processing 11 - 16 May, 1997 Anaheim Ca., USA




Whiteshell Laboratories, Atomic Energy of Canada Limited Pinawa, Manitoba, Canada R0E 1L0


In marketing its IMPELA line of high-power, high-throughput industrial accelerators, Atomic Energy of Canada Limited (AECL) is working with viscose (rayon) companies world-wide to integrate electron-processing technology as part of the viscose manufacturing process. The viscose industry converts cellulose wood pulp into products such as staple fiber, filament, cord, film, packaging, and non-edible sausage casings. This multibillion dollar industry is currently suffering from high production costs, and is facing increasingly stringent environmental regulations. The use of electron-treated pulp can significantly lower production costs and can provide equally significant environmental benefits. This paper describes our current understanding of the benefits of using electron- treated pulp in this process, and AECL's efforts in developing this technology.



Accelerators, 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 of cellulose. 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 conveyor belts, clutch pads, and automotive belts and hoses. In 1995, this multibillion dollar industry produced over 3 million tonnes of viscose materials, and showed moderate (2 to 3%) to major (5 to 10%) growth in production in all countries except Japan (Layman, 1996). The viscose industry is faced with several problems, such as high chemical costs, and environmental pollution. Electron-processing of cellulose prior to its use in making viscose can impact significantly upon these problems. This paper describes the advantages of using electron-treated pulp in the viscose process, 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 2 anhydroglucose residues joined by a -1,4-glycosidic bond (Nevell and Zeronian, 1985). The cellulose polymer chain resembles a flat ribbon, with hydroxyl groups extending laterally from the edges, and hydrogen atoms oriented above and below the plane of the ribbon. This structure allows for extensive interactions between cellulose chains through hydrogen bonding between the hydroxyl groups, and Van der 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 the crystalline regions is very dense, making these inaccessible to reagents and relatively unreactive. Thus, drastic conditions and high reagent concentrations are required for processing cellulose.



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Top View

Crystalline Region

Amorphous Region Cellulose Chains Cellulose Chains Amorphous Region

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 alkali cellulose or AC (Cell-OH + NaOH Cell-0- Na+ + H2O). Due to the inaccessible crystalline regions in 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 or higher. 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). High concentrations (28% to 36%, w/w based on cellulose) of carbon disulfide, CS2, are then added to make a xanthate (Cell-0- Na+ + CS2 Cell-O-C(=S)-S- Na+) containing approximately one ester group for every 2 anhydroglucose residues. This amount of charged, bulky, xanthate groups is sufficient to disrupt the forces holding the chains together in the crystalline lattice formation, thereby promoting solubilization 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 of sulfuric acid, sodium sulfate, and zinc sulfate. During the spinning process, the acid neutralizes the alkali in the viscose and reverses the xanthation reaction. Solid cellulose and CS2 are regenerated, and H2S is produced as a side product (Treiber, 1985). Depending upon the type of spinning dye used, the cellulose is regenerated as fiber, cord, casing, or film. This material is then washed and subjected to finishing 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 is investigating methods for reducing these emissions.








End View

Crystalline Regions









IRRADIATED PULP: ADVANTAGES Irradiation of cellulose causes cleavage of the cellulose chains and formation of more than 12 different radiolytic products (Phillips, 1985; Nakamura et al., 1985). The chain cleavage produced by radiation is precise, reproducible, and can substitute for the aging step in the conventional viscose process (Englund and 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 chemical effects that increase the accessibility of these regions to reagents (Horio et al., 1963; Fischer and Goldberg, 1987). The radiolytic products produced upon irradiation of cellulose differ significantly in structure from their anhydroglucose neighbors, and cannot participate as effectively in the bonding forces that exist in the crystalline lattices. This results in localized defects which weaken the lattice structures, improving their accessibility to reagents. Thus lower concentrations of chemicals such as CS2 and NaOH can be used to produce viscose (Fischer et al., 1980; Fisher et al., 1985; Fischer and Goldberg, 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 less alkali used, less neutralizing acid is required during spinning. For a typical plant, the savings in chemical 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 released into 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 business unit in AECL, to promote the use of IMPELA® , AECL's family of high-energy (10 MeV), high-power linear accelerators, in the viscose process. The Biomass Group has facilities for analyzing pulp before and after electron treatment, for producing viscose at the lab scale, and for assessing viscose quality using standard methods employed by the viscose industry. Collaborations with viscose producers have demonstrated that significant reductions in CS2 , alkali, acid, and zinc can be achieved by using electrontreated 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 Group to optimize plant parameters (dose, amount of CS2, alkali, acid, and zinc, etc.) for using electron-treated pulp. To date, 16 pulps have been evaluated, and processing conditions have been optimized for 3 plants. 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 electrontreated 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 hundred tonnes 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 existing plants. This collaboration will accelerate the process for integrating accelerator technology into viscose plants in the near future. SUMMARY Laboratory and plant-scale results have shown that use of irradiated pulp in the viscose process has the following advantages: 1) significant reductions in CS2, alkali, acid, and zinc consumption resulting in savings 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 substantial environmental benefits; 3) significant savings in pollution abatement costs due to reduced effluent and emission loads; and 4) elimination or shortening of the cumbersome aging step resulting in improvements in process operation and increased throughput.

The Biomass Group is working closely with AECL Accelerators and ING A. Maurer S.A. to promote the use of electron accelerators in the viscose industry. This collaboration is unique in that the Biomass Group 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 more than 25 pulp and viscose companies to demonstrate the benefits of using electron-treated pulp. By the year 2000, several producers will have conducted plant-scale trials and will be in the final stages of implementing electron-processing technology in their plants.

REFERENCES Chincholkar V.S., Mehta L. S., Duveen R. F., Zeller D., Rajagopal S., Stepanik T., Whitehouse R., and Ewing D. (1997) Effect of electron processing on the textile properties of rayon filament yarn. Presented at Cellulose man-made fibres summit. April 22-24, 1997, Singapore. Drozdovskii V. N., Meleshevich A. P., and Stavtsov A. K. (1991) Production of viscose from cellulose - by irradiation with accelerated electrons, treating with sodium hydroxide solution, cooling, treating with carbon disulfide and dissolution. SU patent 1669916. Englund B. E. and Jones J. W. (1957) German patent 1 151 494. Fengel D. (1993) New findings on the fine structure of cellulose. Das Papier 12, 695- 703. Fengel D. and Wegener G. ( 1989) Wood: chemistry, ultrastructure, reactions. 66-105, Walter de Gruyter, New York. Fink H. -P., Hofmann D., and Purz H. J. (1993) Lateral order in microfibrils of native and regenerated cellulose. In Cellulosics: pulp, fibre, and environmental aspects. Kennedy J.F., Phillips G.O., and Williams P.A. Eds, Ellis Horwood, New York, 165-170. Fischer K. and Goldberg W. (1987) Changes in lignin and cellulose by irradiation. Makromol.. Chem., Macromol. Symp. 12, 303-322. Fischer K., Goldberg W., and Wilke M. (1985) Strahlenvorbehandlung von zellstoff für die regeneratfaserherstellung. Lenzinger Berichte 59, 32-39. Fischer K., Wilke M., Goldberg W., and Sendner H. (1980) Process for the production od viscoses. Patents: DE 294114.8 Horio M., Imamura R., and Mizukami H. (1963) Effect of gamma irradiation upon cellulose. Bull. Inst. Chem. Res. Kyoto Univ. 41, 17-38. Krässig H. A., (1993) Cellulose: structure, accessibility, and reactivity. Gordon and Breach Scientific Publishers, Yverdon, Switzerland. Laine J. E., Haukkovaara E., Oraviita P., and Peltola P. (1987) Experimental evaluation of electron beam irradiation and ultrafiltration in the manufacture of viscose fibres. Lenzinger Ber. 62, 54-57. Layman P. (1996) Growth in man-made fibres slowed in 1995. Chem.Eng. News, May 27, 13. Nakamura Y., Ogiwara Y., and Phillips G. O. (1985) Free radical formation and degradation of cellulose by ionizing radiations. Polym. Photochem. 6, 135-159. Nevell T. P., and Zeronian S. H. (1985) Cellulose chemistry fundamentals. In Cellulose Chemistry and its Applications, Nevell T. P., and Zeronian S. H. Eds., Ellis Horwood Limited, Chichester, UK, 15-29. Phillips G. O. (1985) Photochemistry and radiation chemistry of cellulose. In Cellulose Chemistry and its Applications, Nevell T. P., and Zeronian S. H., Eds, Ellis Horwood Limited, Chichester, UK, Chapter 12, 290-311. Rajagopal S. (1995) Overview of electron processing technology of dissolving pulp for the cellulose products industry. Presented at Pulp Electron Treatment and Supply (PETAS), September 25-27, 1995, Hamburg, Germany.

Rajagopal S. and Stepanik T. M. (1996) Status of electron processing technology in the viscose industry. Presented at the Lenzing International Conference: Imagine the Future of Viscose Technology, June 12-14, 1996, Gmunden, Austria. Rajagopal S., and Stepanik T. M. (1997) Unpublished observations. Rajagopal S., Stepanik T., Whitehouse R., Ewing D., Bisaillon P., Tateishi, M., Free, D., Hidasi G., and Poggi T. (1994) Enhancement of cellulose reactivity in viscose production using electron processing technology. Presented at Challenges in Cellulosic Man-Made Fibres, May 30-June 3, 1994, Stockholm, Sweden. Soderlund C.A., (1996) Svenska-Rayon initiates new electron radiation technology in pulp processing. Svensk Papperstidning-Nordisk Cellulosa 99, 27-30. Sokira A. N. and Belasheva T. P. (1992) Effect of gamma-radiation on the physicochemical and technological properties of viscose celluloses. Fibre Chemistry 24, 63-66. Stavtsow A. K. (1996) Possibilities of using radiation modified cellulose in viscose production. Chemical Fibers International 46, 92-94. Stepanik T. (1995) New opportunities in cellulose. IMPELA NEWS 1, Number 2. Stepanik T. M., Rajagopal S., and Saunders C. (1996) Electron processing technology: a novel tool for industrial applications. Proceedings of IUPAC Chemrawn IX world conference on Sustainable Production, Use, Disposal and Recycling of Materials, and The Role of Advanced Materials in Sustainable Development. September 1-6, 1996, Seoul, Korea, 138-146. Treiber E. E. (1985) Formation of fibres from cellulose solutions. In Cellulose Chemistry and Its Applications. Nevell, T.P., and S. H. Zeronian Eds, Ellis Horwood Limited, Chichester, UK, Chapter 18, 455-479. Treiber E. E. (1990) Trends in viscose dissolving pulp and technology. In Cellulose, Sources and Exploitation.. Kennedy, J.F., Phillips, G.O., and Williams, P. A. Eds, Ellis Horwood, New York, chapter 20, 163-168. Ueno T., Murakami M., and Imamura R. (1972) Studies on the manufacture of low DP pulps by irradiation (Part 5) "no-aging' viscose process for irradiated pulps. Japan Tappi 26, 164-172. Wolschner B., Weber H., von Linde F., and Peritsch M. (1995) Cellulose fiber industry - economic and ecological aspects of further developments. Chemical Fibers International 45, 41-43.


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