Viscose rayon: recent developments and future prospects. John Dyer, and George C. Daul. Ind. Eng. Chem. Prod. Res. Dev. , 1981, 20 (2), pp 222â230. DOI: 10.1021/i300002a004. Publication Date: June 1981. ACS Legacy Archive. Cite this:Ind. Eng. Chem.
in 1892 by Cross, Bevan, and Beadle. This discovery came as a new andgreat inspiration to the study of cellulose chemistry and to the com- mercial utilization of ...
The problems arising in the manufacture of viscose rayon are of a mechani- cal and chemical nature and may be divided into two groups, uiz: those re- lating to ...
Table I. Cellulose Samples for. Fractionation. Identifying Letter for Both Pulps. Pulp. Rayon ..... fractionation, precision of viscosity determinations,and thor-.
Table 1. Analytical Data for Sodium Lignate and Sodium. Lignosulfonate. Sodium ... Corrected denier. Control. 20% Sodium lignate k0% Sodium lignate. Control.
Future Commercial Prospects for Synthetic Rubber2. William C. Geer. Ind. Eng. Chem. , 1926, 18 (11), pp 1136â1137. DOI: 10.1021/ie50203a011. Publication ...
Calculate AI' by means of Equations 2c, ;3c, 5c, or 6c, using the equivalent diameter and actual velocity. VISCOSITY. In all the above equations, viscosity is ex- pressed in centipoises, as most data in the literature are generally given in terms of
Clarence W. Balke. Ind. Eng. Chem. , 1938, 30 (3), pp 251â254. DOI: 10.1021/ie50339a003. Publication Date: March 1938. ACS Legacy Archive. Note: In lieu of ...
The Manufacture of Chloroform from Bleaching Powder and Ethyl Alcohol. Journal of Industrial & Engineering Chemistry. Frerichs. 1912 4 (5), pp 345â352.
Aug 7, 2015 - Manufacturing & Materials Technology Area, Toner Development & Manufacturing Group, Xerox Corporation, Webster, New York 14580, United States. Ind. Eng. .... Emulsion phase inversion of model and crude oil systems detected by near-infra
Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 222-230
Table III. Application of Cumulative Model for Soil Cadmium in a Hypothetical Example to Determine Predicted Project Lifetime annual nitrogen need nitrogen in sludge annual applied sludge annual applied sludge cadmium in sludge annual applied cadmium EPA cadmium soil limit
Downloaded via IOWA STATE UNIV on January 23, 2019 at 08:52:38 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
cumulative model slope for cadmium lifetime applied cadmium lifetime applied cadmium annual applied cadmium project lifetime
10 mT/(ha/year) 50 mg/kg
(kg/ha) 77 kg/ha
77 kg/ha 0.5 kg
It is not possible to project the results from one soil type to another. The results of these projections would also be sensitive to the type of sludge used and to the type of crop grown. Another major constraint is the apparent lack of relationship between either cumulative or annual sludge application and whole plant tissue concentrations. Thus,
these models appear applicable for projecting project lifetimes based on soil metals concentrations but do not appear to be useful for projecting plant tissue burdens. Balrer, D. C. "Soil Enrichment Study 1974 Row Crop Field Trials”; (Progress Report No. 3) East Bay Municipal Utility District, Oakland, CA, 1975. Burpee, L.; Osborn, K. E.; McLean, D. A. “Soil Enrichment Demonstration Project, Novato Sanitary District", San Francisco Bay Region Wastewater Solids Study, Oakland, CA, 1979. Capar, S. G.; Tanner, J. T.; Friedman, M. H.; Boyer, K. W. Environ. Sol. Technol. 1978, 12, 785. Council for Agricultural Science and Technology, Report No. 64, Ames, IA, 1976. Hyde, H. C.; Page, A. L.; Bingham, F. T.; Mahler, R. J. J. Water Pollut. Control Fed. 1979, 51, 2475. Hyde, H. C. Presented in part at the 48th Annual Conference, California Water Pollution Control Association, Lake Tahoe, CA, April 1976. Lindsay, W. L. Adv. Agron. 1972, 24, 147. Osborn, K. E.; McLean, D. A. “Soil Enrichment Demonstration Project, Solano County", unpublished data. “San Francisco Bay Region Sludge Management Plan"; San Francisco Bay Region Wastewater Solids Study, Oakland, CA, 1978.
Received for review October 9,1980 Accepted February 23, 1981
Presented at the Second Chemical Congress of the North American Congress, Las Vegas, NV Aug 25-28, 1980.
Symposium on Recent Advances in Viscose Rayon Technology G. C. Daul, Chairman Second Chemical Congress, Las Vegas, Nevada, August 1980
Viscose Rayon: Recent Developments and Future Prospects John Dyer* and George C. Daul ITT Rayonier Inc., Eastern Research Division, Whippany, New Jersey 07981
By the end of the 1970’s, viscose rayon was recovering and consolidating its position in the marketplace following a period of decline partly attributable to competition with and an overabundance of synthetic petroleum based fibers. Now a number of rayon markets such as fashion fabrics and nonwovens are experiencing strong growth. Improvements in present manufacturing processes together with the development of improved fibers such as high
crimp HWM, Modal, hollow fibers, flame retardant, highly absorbent, and alloy-rayons have shown the versatility of the viscose rayon process. Rayon enjoys a unique position as a textile fiber in that it can be tailored to fit numerous end-use applications. Today's rayons offer superior performance alone and in blends with other fibers such as polyester, wool, and cotton. Considering the availability of raw materials and the need to feed a growing population, viscose rayon will assuredly remain as one of the most versatile, engineered fibers in the foreseeable future.
It was more than 12 years ago at the Second International Symposium on Viscose Technical Questions that a statement was made that the viscose process had reached a state of development which left scarcely any room for the discovery of new or superior properties by economically feasible methods (1). There have been many improvements on both counts since then and the total world production of rayon has been maintained at 6-7 billion pounds per year (Figure 1) fluctuating according to the economic climate in producing countries (2). In the past decade production in Western Europe, the United States,
Table I. Relative Raw Material Cost/lb Percentage of Rayon List Price
1970 1975 1980
35.7 34.5 34.2
14.3 12.7 13.2
10.7 10.9 11.8
28 55 76
Energy Equivalence for Fiber Production kg of oil/kg of fiber raw
rayon cellulose acetate polyester nylon 66 acrylics cotton
ever, this type of investment was incidental to the production of rayon, involved added operating costs, and diverted capital from much needed capacity expansions
and improvements. Despite these difficulties, major rayon producers have improved the efficiency of their operations, closing unprofitable facilities and consolidating the product mix to meet projected demand in markets where stability and growth are expected. In the past four years, production in most countries has increased from the 1975 lows including the USA where the recovery has amounted to more than 35% over 1975 production. Today viscose rayon is produced in 42 countries at 115 plants by more than 100 producers excluding those in the USSR, China, and North Korea (3). Desirable qualities of rayon and advances in viscose technology have enabled the viscose rayon industry to sustain its place in the world fibers market. In this article, reference will be made to literature publications and information that has become available since the reviews by Clayton (4) and by Wallace (5) were published in 1976 and 1977, respectively. First, “recent developments” should be put in perspective since most of the advances in viscose rayon technology represent the result of R&D often over extended periods of time. It was Hooke, in 1664, who first suggested the idea of preparing artificial fibers, but it was not until 1855 that the first patent for making “artificial silk” was granted to Audemars. This beginning led to establishing cellulose as the first man-made fiber industry around the turn of the nineteenth century (6). The exciting years of 1900-1965 saw many advances in viscose rayon technology, and the industry expanded. However, it was the discovery of nylon and other synthetic polymers that could be melt-extruded into fibers in the latter half of this period that captured the imagination of researchers. Interest in cellulose waned, and in many cases, profits earned by rayon were invested in synthetic fiber plants. Then, in the late 60’s and 70’s, with the growing awareness of finite oil reserves and the need to conserve energy, it was considered that available fiber polymers were largely adequate. The search for new polymers by industry, for other than special applications, was all but discontinued in preference for the more urgent need to reduce cost and improve properties and quality of existing fibers. Albrecht (7), at an international symposium on manmade fibers in Kalinin during May 1975, in reviewing the process of producing fibers from cellulose, stated that “research should not be carried out blindly and that the
3.388 1.694 3.222 4.065 2.472 0.316
1.30 2.649 0.935 1.114 3.263 0.814
4.7 4.3 4.2 5.2 5.7 1.1
results must prove themselves with other fibers and constantly improving technologies.” To a large extent this has been and continues to be accomplished. Today, R&D on the viscose rayon process is now mostly conducted based on industry needs and market opportunities. What, then, were these needs to which researchers had to direct their efforts? Broadly they fit into three areas: (1) raw materials (2) process technology, and (3) products, with a number of principal objectives related to economics, environment, and markets. Rayon had to compete not only with cotton but also with the glamor products of the synthetic polymer research era which have, until recently, enjoyed a number of advantages especially in cost and durability that enable them substantially to erode rayon’s position in the market place. It was, for example, the price differential between polyester and rayon existing during the early 70’s that contributed to the decline in rayon use for diaper cover stock. Then there is the familiar situation with the U.S. tire cord market where rayon use has steadily declined from 63% of total (229 X 106 lb) in 1960 to less than 6% in 1979. Over the past 10 years the list price of rayon has roughly paralleled raw material prices as quoted in Chemical Marketing Reporter (Table I). Obviously, a number of very important factors must be considered here such as the price of competitive fibers, cotton and synthetics (8). In fact, to a large extent, the price of cotton and polyester have determined the economics of the viscose rayon industry. But the significant factor is that although raw material manufacturers are faced with the same economic difficulties—environmental protection, energy, labor, etc.—as the rayon producer, the cost of pulp as a percentage of rayon list price has not changed appreciably. Perhaps the greatest relative increase in rayon manufacturing cost has resulted from rapidly escalating energy costs and labor. Even with conversion from oil to coal the cost is substantial, and in some parts of the world, such as India, there are insufficient energy resources available to operate rayon production facilities on a continuous basis. Although the viscose rayon process is energy intensive, when all the energy consumed in producing the fiber and raw materials and the heat content of any material that could otherwise be burned as fuel are considered, the total energy equivalence of rayon compares favorably with other synthetic fibers (Table II) (9,10). Data from the Textile Economics Bureau show that energy conversation measures by the textile fiber industry have reduced the total energy consumed to produce various fibers. Part of the improvement shown in recent years can
attributed to the increased utilization of existing facilities available for fibers production. Also, it has been claimed that when fertilizers, pesticides, and energy required to care for finished garments are included, cotton be
is more energy intensive than polyester and dependent on petrochemicals for growing, harvesting, and purification
Reduction of raw material consumption in viscose production has been a principal objective for research in the past. Improved economy can be derived by any one or combination of lower CS2, lower caustic, and higher cellulose in viscose. The use of lower cost pulp to make high performance rayons is generally not attractive since the increased cost of processing into acceptable quality rayon usually exceeds the cost saving on the pulp. There are a number of ways to achieve a reduction in the amount of CS2 used to make viscose. The most notable
of these is the double steeping process developed by Sihtola and Nivosky which also allows a substantial reduction in viscose alkali content (12,13). A second steep after aging the alkali cellulose is used to reduce the amount of free alkali in the crumb without changing the bound alkali. In this way not only is xanthation more efficient since less
byproduct is formed at the lower free alkali concentration, but the distribution of xanthate groups is improved and a more stable viscose is obtained. The SINI process can yield a 30% reduction in CS2 usage substantially reducing H2S emissions. However, it requires added steeping and alkali cellulose handling capacity and consequently is of limited interest where existing capacity is fully utilized. A review of double steeping was published in 1979 (14). The various economic aspects and details of process evaluation at a rayon facility have also been described by Sihtola. Most recently, another double steeping patent in which the second steep is performed on unaged alkali cellulose has been issued to Enka (15). The patents of Geyer and White, who were previously associated with the American Viscose Corporation and are now with Fiber Associates Inc., deserve some mention. In these they describe a process for xanthation (16) and more recently a process and apparatus for making alkali cellulose in sheet form that utilizes RF energy to achieve the required cellulose depolymerization (17). Again, irradiation of cellulose by y rays or accelerated electrons had been proposed as a way to eliminate the alkali cellulose aging step of the viscose process. It had been demonstrated that substantial improvement in viscose quality (filtration) could be achieved by this technique and Du Pont obtained a number of patents for an “Improved Viscose Process” utilizing radiation (18). Later work by Ueno et al., published in 1971, suggested the use of irradiated pulp in a no-aging viscose process (19-23). Of significance in this process was the fact that the cellulose depolymerization occurred by random scission and required only a very short time, on the order of seconds, compared to the hours required by the conventional process. Alkaline hydrolysis (end group attack or peeling) of the cellulose molecules was eliminated with resulting substantial benefits to the final rayon yield. However, problems with high alkali solubility of irradiated pulp complicated the steep liquor recycle and, in addition, the high content of carbonyl groups formed by free radical oxidation during irradiation, led to color generation in the rayon fiber necessitating bleaching to produce an acceptable product in some cases. There is some evidence that irradiation improves cellulose reactivity and accessibility since depolymerization occurs equally in crystalline and amorphous regions of the cellulose unlike chemical depolymerization, which occurs
primarily in the accessible areas (24). However, the process has not been adopted commercially possibly either because
capital was not available or the production volume was not sufficient to justify the switch and the work necessary to overcome the above problems. It is suggested that the process might be reconsidered if new grass roots rayon facilities are planned. Activation of cellulose with liquid ammonia prior to (25) xanthation also reduces CS2 consumption by as much as 33%. An increase in the amorphous portion of the activated samples was confirmed by X-ray examination. Ammonium hydroxide (>45%) was not as effective as liquid ammonia, providing only a 10% increase in reactivity. Urea can also be used as a pretreat to obtain improved reactivity (26). The effect of hemicellulose content in steep liquor continued to receive attention and is considered of particular importance in the manufacture of high performance rayon (27). Adverse effects of hemicellulose on viscose ripening and viscosity, filtration, and fiber properties such as alkali solubility, color, and dyeability are well documented. Substantial problems can also be encountered with yield and BOD related to the hemicellulose level in the process. Overcoming these deficiencies has also been an important objective for viscose research (28). The formation of short-chain cellulose by catalytic degradation caused by metals such as iron is also undesirable in the manufacture of rayon. A German patent to Hoechst describes the use of complexing agents like EDTA or sodium polyphosphate added to viscose to suppress the action of trace metals (29). Xanthation in the presence of surfactants like Berol’s spin 641 has been claimed to decrease the CS2 consumption without affecting the quality of rayon produced (30). The efficiency of xanthation is reportedly improved by the surfactant (31). Beneficial effects of surfactants in the viscose process using appropriate conditions are well known (32). Recently, attention has been given to removing surfactants from rayon process waste streams (33-35). In another article it is reported that surfactants reduce viscose viscosity which could be important where high cellulose viscose is being processed (36). Investigations of viscose ripening have been reported in Khim. Volokna (37). Atmospheric oxygen had no significant effect on the rate of change of cellulose xanthate DS (7) but it did decrease the amount of polythio compounds in viscose (38). Sodium sulfide had no appreciable effect on viscose ripening while sodium sulfite significantly retarded the physicochemical reactions (39). Much of this work appears to duplicate studies made by other investigators such as Danilov several decades ago. However, the data could have been required to develop improved process control for the manufacture of rayon such as reported by Klokov et al. (40). A continuing goal for research is improved viscose quality. Apart from the improvements derived from increasing the efficiency of steeping and xanthation by chemical means, the subject of viscose filtration has continued to receive attention (41-44). Operating experience with the Funda filter and the recently developed Viscomatic filter (45) is becoming available and, as expected, confirms that benefits can be obtained from using such equipment. Not only is viscose quality important to filtration cost and spinning, but the nature of the viscose and its particle content are of profound importance to the fiber properties (46). Very little is known of how viscose particles affect fiber structure and this is a subject being investigated at
Rayonier’s research laboratories. Although incomplete, results from this work suggest that particles behave differently to the viscose matrix during extrusion and regeneration leading to structural nonuniformity in the fiber. Filicheva et al., investigating the effect of free NaOH content in viscose on its properties, have shown that decreasing the viscose alkali content adversely affects viscose quality (47). It was suggested the NaOH/cellulose ratio should be lowered by adding more cellulose to the viscose rather than by decreasing the NaOH content. One problem envisaged with this approach was the increase in viscose viscosity. In a later publication on ways of reducing the consumption of materials in the production of viscose rayon, the problem of viscosity was addressed (48). Three methods of reducing viscosity were considered: (1) increase temperature, (2) increase shear, and (3) reduce degree of polymerization (DP). Production conditions at the Klin combine, as in most viscose rayon plants, dictated selection of the third method and investigations were made to establish the lowest DP from which acceptable fiber properties could be obtained. Tenacity varied only marginally with DP above 280-300. By a combination of increasing cellulose in viscose to a lower caustic/cellulose ratio and reducing the cellulose DP, cost savings equivalent to 159 kg of caustic and 196 kg of sulfuric acid per ton of rayon were achieved. Growth of HWM rayon relative to polynosics is associated with simpler and more economic manufacturing methods. High wet modulus fibers are less stiff and do not tend to fibrillate as readily in the wet state. Economic factors such as market price of competitive cotton and synthetic fibers has perhaps been the most significant reason high performance rayon production has not expanded more rapidly. Wet modulus is a very important property for end use performance. Whereas only a few years ago it was considered that some strength could be sacrificed to achieve the high wet modulus, advances in conversion technology (staple to yarn) such as open-end spinning and especially in blends with synthetic fibers, required adequate rayon properties. The use of formaldehyde to achieve high wet modulus is well known (49). However, in recent years concern over the possible toxicity of this chemical has led to increasingly stringent regulations on workers exposure (50). Although agents that generate formaldehyde on exposure to acid have been examined, they are generally less effective and in most cases still cause problems with spin bath precipitates and contaminated reclaimed sodium sulfate. The effects of various spinning conditions and viscose compositions on the properties of modified viscose fibers were discussed by Treiber in a 1978 paper published in Faserforschung und Textiltechnic (51). Increased spiraling speed is recognized as one way to reduce costs, but so far little success has been achieved for high performance rayon (52). Instead, the approach that has been adopted uses cluster-jets (53,54) with as many as 70000 filaments being produced from a single assembly of smaller spinnerettes. A series of papers published by Kawai and co-workers describe studies on wet spinning as it relates to the production of polynosic fibers (55-57). This work, also published in 1978, examines various aspects of the process such as the relationship between coagulating bath conditions, composition, viscose feed rate, spinnerette hole diameter, spinning and stretching conditions on the structure, and properties of the fiber. The type of spinnerette used can have important effects in viscose spinning. Thus, it has been shown that increasing the length:diameter ratio of the spinnerette hole yields more uniform fiber denier
(58,59). Spinnerettes made of 92.5% platinum and 7.5% gold had smooth mirror-like surfaces and required less frequent changing due to a substantial reduction in fiber defects (60,61). A method for manufacturing viscose filaments involving dry spinnerette-wet spinning of well-ripened viscose is the basis of a 1978 U.S. patent to a group of French researchers (62). Although the concept of gel spinning is not new, it is receiving attention because of the substantial economics offered by high cellulose concentration. In this, the development of anisotropic spinning solutions of other polymer systems (polyaramids, etc.), in which at high concentrations the polymer molecules become organized in liquid crystal arrays, is of interest. It has been shown, for example, with cellulose acetate, that the short-range liquid crystalline order existing in the solution prior to extrusion leads to the formation of fibers having greatly improved strength (63). The possibility of deriving advantage from this in the production of viscose rayon would require much higher concentrations of cellulose to achieve the anisotropic state in viscose and is complicated by the chemical instability of the system (64). U.S. patent 4159 299 names 20 inventors of a method for the production of rayon in a vertical spinning column consisting of two separate portions in which coagulation, regeneration, and stretching are completed (65). An extensive review of patent literature (1924-1977) on wetspinning in vertical tubes was published in 1978 by Korotkov et al. (66). Additional control over gas evolution that such systems provide can be used to advantage. A series of patents issued to Avtex resulting from the work of Smith (67) describe alloy rayon fibers having a range of unique properties (68). This development is based on the concept that the properties of a material compatible with viscose could be used to enhance the properties of rayon fiber. Typical of this would be the inclusion of carboxymethyl cellulose (69), starch (70), poly (vinyl pyrolidone) (71), polyacrylamide, or polyacrylic acid (72) in rayon by mixing the material with viscose prior to spinning. Substantial improvements in moisture absorption (73) and dyeability were achieved by this technique and the alloy rayons are currently used in a number of consumer products (74). Earlier work by Wizon (75) had produced ceramic fibers by inclusion of an inorganic filler in the rayon structure prior to pyrolyzing to obtain a fiber that was useful in high-temperature environments. More recently the use of sodium silicate in viscose has been described again in a Polish patent (76). Avtex were not alone in the development of new and improved viscose rayon technology based on incorporating various materials in the fiber structure. Enka, for example, have obtained patents for a highly absorbent fiber using polymers of acrylic acid and related materials (77) and copolymers of alkyl vinyl ether and ethylene dicarboxylic acid (78) added to viscose as alkaline salts. Also in 1977, Franks, who was at that time with Enka, described a
process by which lignin was used as a viscose filler (79). However, the use of lignin poses no real advantage in the manufacture of viscose rayon because the fiber tenacity is reduced and the economics would be little different, perhaps worse, than using cellulose since the materials are derived from the same source. The presence of lignin residues in pulp is known to adversely affect viscose quality and spinning, and where chlorinated components are involved, these can lead to substantial acidic degradation of the fiber on exposure to heat. With the introduction of Viloft (80) and Avril II (81) in 1977 and the development of Prima (82), hollow fibers and
crimped fibers became established as providing improved cover and performance in fabrics. Promotion of these fibers began the current era of rayon renaissance (83). The search for improved performance continued leading to further advances (84). One such development is based on the work of Costa who, from an extensive factorial study, developed viscose compositions and spinning conditions yielding high strength hollow rayon fibers (85). Inflation was achieved by using sodium carbonate. A patent issued in December 1978 gave examples showing the hollow filament which did not collapse after washing and drying possessed strength almost equivalent to that of HWM rayon. In a subsequent patent issued to Costa and Godsay of International Paper Co. in January 1980 on the Production of High Crimp, High Strength, Hollow Rayon Fibers, changes in composition and spinning conditions yielded more than 20 crimps/in. in the hollow fiber (86). Hollow fibers for dialysis and ultrafiltration were prepared from viscose and examined by Groebe et al. (87). Although the fibers possessed different ultrafiltration properties no relation between the separating power and the fiber structure could be established by electron microscopy. Bulky and uniformly hollow rayon fibers were prepared using up to 10% oleic acid (boc) added to viscose as described in a 1978 Japanese patent (88). However, the fibers were weak. Other developments in hollow fibers will be mentioned later. At the seventeenth conference on man-made fiber technology in Leningrad during May of 1978 Rogovin indicated that a number of developments were ready for pilot-scale evaluation (89). These included: (1) increased output of chemically modified viscose rayon stape (Mtilon and Tsevalan) (90) and (2) ion-exchange fibers based on chemically modified viscose rayon staple (91). For economic reasons it was necessary to recycle viscose waste from each stage of the viscose process with accompanying adverse effects on quality and product properties. Such waste viscose could be processed into sulfide containing fibers which do not need good physicomechanical properties to be used for ion-exchange applications (92). Modification of rayon fiber properties can also be done by chemical treatments after spinning such as an afterstretch in liquid ammonia (93). Grafting other materials onto the cellulose by various techniques such as the thiocarbonate-redox process developed by Scott Paper Co. (94), or irradiation (95), have been extensively studied. Cross-linking affords another way to modify rayon fiber properties and is the basis of resin treatment to obtain wrinkle resistance for fabrics containing rayon (96-98). In general, however, such approaches to modify rayon properties (99) are much less desirable than obtaining the required characteristics in producing the fiber. No review of viscose rayon technology would be complete without mention of spin bath reclaim and pollution abatement (100). Both are important to process economics albeit in different ways. A great deal of work has been done monitoring CS2 and H2S emissions not only within rayon producing facilities (101-104) where the gases could pose health and safety problems (105), but also on the extent of atmospheric
pollution (106). It has been estimated that each year
more than 220 million tons of sulfur are introduced into the atmosphere from various natural and industrial sources (107). Only about 0.4% of this amount could come from the viscose process if there were no CS2 reclaim. Although gases released from the viscose process have a relatively short half-life in the atmosphere, their eventual fate as a sulfate
aerosol contributes to acid rain. In addition, the problem
at the very low concentrations normally that has required considerable attention. In the viscose rayon industry the volume of ventilation air required to maintain a safe working environment (108) is high. Scrubbing exhaust gases (109) under these conditions is impractical. Adsorption is the most frequently mentioned process for CS2 reclaim with adsorbents ranging from mineral oils (110), and natural zeolites (111) to activated carbons (112) and anion exchangers (113). Condensation affords a convenient, relatively trouble free, economic way to recover CS2 when the gas stream is sufficiently concentrated such as emissions from the cutter and sluice where almost 40% of the available CS2 can be generated. Determination of points of the greatest formation of CS2 and H2S in rayon fiber production has been reported by Gasyuk et al. (114). Hydrogen sulfide generated during spinning originates primarily from viscose byproducts such as sodium trithiocarbonate. The presence of H2S in exhaust streams complicates CS2 recovery since the sulfide is oxidized on activated carbon to sulfuric acid which destroys the absorptive capacity of the carbon bed (115,116). Trithiocarbonate decomposes much faster than cellulose xanthate during viscose spinning and consequently most of the H2S generation occurs in the spin bath where it can remain dissolved and be carried to the spin bath degasser for removal (117,118). Absorptive spin baths have been examined for this purpose (119). The suggestion of reducing byproduct formation in viscose preparation (120) to achieve a reduction in H2S generation during spinning has a drawback in that the trithiocarbonate functions as a modifier affecting the rayon fiber structure and properties (121,122). This has been shown by the reduction in skin formation that occurs if the byproduct is removed from the viscose before spinning, and also in the rate of acid diffusion through viscose films, work done at Rayonier’s Research Laboratories. Quite a number of articles in the literature report on various aspects of spin-bath reclaim (123,124), zinc recovery (125-128), and treatment of process effluent to reduce BOD, COD etc. (129,130). Again, the majority of these papers are to be found in Russian journals and, with few exceptions, appear to relate mostly to operating experiences and information about existing technology. To a large extent the ideal viscose rayon facility will not only produce better quality rayon but do so consistently with efficient recycle and reclaim of chemicals. Systems are being examined to cut back on the volume of spin bath and processing solutions, reduce ventilation air, increase production, and more effectively utilize energy for the various process steps. According to an article by Fueg (131), Maurer has developed a new generation of staple fiber spinning machines that accomplish many of these objeceven
Substantial reductions in polluting emissions from the Kalinin rayon plant have been reported. The zinc content of the Volga River apparently now meets standards for fishing. During the period 1975-77, zinc in purified effluent was reduced 2.5-fold, suspended substances decreased by a factor of 4, and CS2 and H2S emissions substantially lowered. These effects were attributed to the use of lower cost viscose—presumably containing less CS2 and caustic, more efficient filtration, and improving mixing. Complete recycling of purified effluent at the Kalinin facility is expected by 1981 (132). The previous section of this review has been about factors associated with the production of viscose and rayon.
2. New rayons, scanning electron micrographs showing cross-section shape: a,
Recent developments from the standpoint of products available in the marketplace are reviewed in this next section. In the past five years rayon has gained a new image (133-135). Although in the United States rayon promotion is still hampered by the restrictions of the FTC definition of the fiber, terminology adopted by the International Standards’ Organization in 1975 designating regenerated cellulose fibers with wet tenacity of at least 2.5 gpd at maximum 15% elongation as Modal (136,137) has provided a means for promoting consumer identification of the changed/improved fiber properties. The viscose rayon process is remarkably versatile and it is possible to obtain regenerated cellulose fibers having structures and properties to fit more end-use applications than with any other man-made fiber (138). Obviously this is not sufficient justification for commercial production of each rayon variant where market volume and contribution margin become determining factors. Nevertheless, the R&D efforts and results, and the inherent advantages of cellulose-based fibers, have made and will continue to make important contributions toward the “Rayon Renaissance” (139). According to some estimates more than 50% of the commercial high wet modulus rayons produced today were not available five years ago (140). Thus, in the past five years a number of new cotton-like viscose rayon fibers have been introduced to the textile market: Courtauld Ltd’s. Viloft, ITT Rayonier’s Prima, and Avtex Fiber’s Avril III. Each of these has taken a .
b, cotton; c, Prima; d,
different approach in the aim toward cotton likeness (Figure 2).
Viloft was described at the ACS Meeting in March 1977 (141). This fiber has been engineered to have a hollow center similar to the lumen in cotton, but larger and hollow when wet. It is less dense than ordinary rayon confering
better cover power in fabric. Prima adds high bulk and softness to fabrics as a result of its spiraled bilobal cross section and fine, low amplitude crimp (142-146). This fiber has high strength, a high wet modulus and extremely good resistance to caustic soda. Prima technology has been licensed to a number of rayon producers worldwide including AVTEX, SN1A, SNIACE, and SATERI. Avril III, first introduced in 1978, draws its uniqueness from a modified multi-lobal cross section and a dulling agent intended to give opaqueness to fabrics and a more cotton-like, crisp hand (147,148). New developments in viscose rayon are also having an impact in the area of nonwovens (149-151). Improved absorbency obtained from the alloy fibers mentioned earlier, which incorporate hydrophilic materials in the rayon structure, make the fibers particularly suitable for applications in hospital/medical and sanitary products (152). Typical fibers that have become available are Enka’s Absorbit (153), Avtex’s PA rayon (154), Lenzing’s Quel (155), and Courtauld’s SI fiber (156). This latter fiber extends Viloft technology into the domain of “SuperInflated” fibers and since it is 100% cellulosic poses little
problem in gaining approval for health-related applications. Spun-bondeds have been a most successful growth area for nonwovens in the last decade (157). Although a number of companies developed spun bonded rayon (758) such as Tachikawa’s Polybonic process and Mitsubishi’s TCF (Textiles Continuously Formed) (159), apart from Futamura very little commercial development has resulted. It is reported that Courtaulds are piloting a process to produce spun-laid rayon including a variety based on SI fibers (760). The spun-lace process developed by Du Pont (161) a number of years ago utilizing 1007c rayon has a number of drawbacks including cost and poor strength uniformity across the fabric compared to in the machine direction. Although finish can affect spun-lace properties, obtaining improvements in this way can detract from a principal advantage of the spun-lace, viz. sheet integrity is obtained by fiber entanglement without the use of a binder (762). To meet specialized markets which have developed in recent years, many rayon producers have introduced modifications of rayon which had been “on-the-shelf ’ as the product of past research while still others have undertaken R&D of totally new systems. Introduction of such products had to wait for the opportune time in terms of existing products and changing market needs and opportunities. One such market that developed as a result of the National Flammable Fabrics Act was for flame retardant fibers. Rayon is capable of being produced with flame retardant additives in situ compared to cotton where flame resistance is normally achieved by topochemical treatments (163). Concern over leaching of FR agents that might have toxic, carcinogenic, or other health hazards together with the relatively high cost of FR additives which must be included at high concentrations in the fiber to be effective, has limited commercial production (164). The tris scare of a number of years ago, which led to the withdrawal of several effective flame retardants, provided reason for more extensive screening of FR fibers not only adding to cost but slowing introduction (765). To some extent imposition of FR regulations on the textile and apparel industry has attenuated (766). Even so, publications related to flame retardance represent by far the largest volume of work reported in the literature about rayon products (167). And, most recently, there has been a resurgence of market interest and need for flame resistant fibers. A number of FR rayons—Avtex’s PFR, Daiwabo’s HFG, Kanebo’s Bell Flame, and Lenzing’s Flamgard, to name a few are produced to meet this need (768). Another development is Enkaire, a flat crenulated cross-section fiber produced by Enka for blending with polyester or acrylics to produce sweater yarn. This particular cross section (Figure 3) of 15 denier filament provides a coarseness to the fiber hand which resembles that of wool. It is also claimed that Avril II, a crimped fiber which was introduced in 1977 by Avtex, feels like wool (769). The viscose rayons of today have evolved from one of the first man-made fibers. Rayons initial dominance of the man-made fiber industry was eventually challenged by newer synthetic fibers and in 1967 world production of synthetic fibers equalled cellulosics at about 3.5 million tons. By 1979 synthetics production had increased to almost 11 million tons with little change in the cellulosics although a decline in continuous filament was balanced by increased staple fiber production. A significant change in rayon end use patterns occurred, which, when the constraints of the past decade are considered, reflects the
versatility of the fiber and the viability of the viscose rayon process. To have weathered the problems of market loss to synthetic fibers, competition with subsidized cotton and the various regulations imposed by government agencies suggests that rayon could experience strong growth in the future. Thus the particular attributes of viscose rayon production that would support such a prediction include: (1) availability of raw materials (a) cellulose—nature’s renewable polymer, (b) CS2—recoverable to a large extent, (c) sulfuric acid and caustic soda—normally in large supply; (2) nondependence on oil; (3) price stability and product quality relative to cotton; (4) major investments for environmental compliance have been made; (5) proven performance in end-use. Although it might be more appropriate to use synthetics in some applications such as tires, belts, and fishing lines, where the fibers possess strength and durability advantages over cellulose, for mass produced consumer goods—wovens, nonwovens, knits, etc., cellulose would be the preferred fiber for reasons of comfort, with rayon having a number of advantages over cotton, viz.; availability and price stability, physical properties suitable for wide range of textile uses, excellent mill processability, no dust problem, and compatible in blends with a wide range of fibers. From projections of World population (170) and per capita fiber consumption (7 77), it has been predicted that by the year 2000, man-made fiber production would reach 25-30 million tons per year. A number of assumptions have been made to obtain the projected world textile fiber demand shown in Figure 4; per capita consumption, cotton, wool, and other fiber production remain at about 1979 level although it is probable that as the world population increases, arable lands will be required for food crops at the expense of cotton. Superimposed on these data are two complete possible cycles of world crude oil production according to the projections of Hubbert (172). One projection, peaking around 1995, assumes a smooth rise and decline without major disturbances, and the other projection assumes production rate is held at about 20 billion barrels per year. This second case probably more closely
reflects the present situation. Taken as a whole, the fiber industry utilizes only about 0.5% of the crude oil production for raw materials. On a short term basis, the next 25 years or so, a substantial increase in synthetic fiber production would have no significant impact on oil consumption in the first case and only minor impact for the second case. However, neglected from this consideration is the changing pattern of oil consumption associated with the growing population and the development of alternative energy sources. It is within this time framework, the next 25 years, that major changes will occur in the world’s fiber supply distribution which will be most important to long-range projections. Crude oil is still the best source of raw materials for synthetics, but it is subject to rapidly increasing price, availability, and eventual depletion. On the other hand, rayon is derived from an abundantly available raw material, cellulose which is obtained from a replenishable source—trees. Can there be any question about its future?
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Received for review September 9,1980 Accepted February 11, 1981
Contribution No. 200 from the Eastern Research Division of ITT Rayonier, Inc. Paper presented in a Symposium on “New Developments in Viscose Rayon” to the Cellulose, Paper, and Textile Division at the 180th National Meeting of the American Chemical Society, Las Vegas, NV, Aug 1980.