I
W. J. ALEXANDER and R. D. KROSS Eastern Research Division, Rayonier Inc., Whippany, N. J.
Surfactants in Viscose Processing Selected surfactants applied to cellulose raw material can provide many processing benefits without contaminating the finished product
SERFACE
active additives are used extensively in the rayon and cellophane industry to improve viscose processing performance and runability of the freshly extruded fiber or film end products. Ideally, they should be added prior to steeping, along with the chemical cellulose. Carefully metered applications as a treat on the cellulose raw material ensure uniform distribution in all the subsequent viscose processing steps without inconvenience or need for special analytical control on the part of the cellulose user. Of a wide variety of compounds which have been investigated, only a few are really useful. Frequently a material may perform a single function well in some stage of processing but be ineffective, unstable, or even detrimental a t some other stage. Furthermore, it is essential that any added agent does not remain in the finished product as a n undesirable contaminant. For rayon, no treat residue should remain to cause color development, impair dying properties, or damage fiber strength. For film, which may be used for food wrap, there is the additional requirement that it be entirely free from toxicity. In the following discussion, the viscose process is considered step by step with regard to the role played by surfactants, their stability i n the chemical environment, and the amount retained for ensuing steps. T h e surfactants employed in this study are identified in Table I. They were applied to the chemical cellulose as strip treats.
transfer as well as formation of colloidal emulsions. T h e relative stability in steep liquor of several surface active treats is shown in Table I. Although five of the six treats compared showed no marked decomposition, many surfactants d o not possess this high resistance to saponification or decomposition. I n the conventional sheet steeping operation, surface active additives serve no particularly useful purpose. However, in slurry steeping they may reduce foaming, floating, and clumping (Figure 2). T h e effectiveness of surfactants in this capacity varies widely, from the excellent dispersion produced by nonionic 1 to the poor result obtained with anionic 1.
Alkali Cellulose Shredding Following steeping, pressed alkali cellulose is shredded. A benefit to be realized from additives a t this point, particularly with certain high purity pulps that are extremely low in native resin content, is a reduction in the power requirement needed to shred the material. Probably because of fiber lubrication, the sheet structure is easier to tear apart into a uniform, open, and highly accessible crumb without excess fluffiness.
Figure 3 illustrates this effect for a sulfate pulp. T h e reduction in power requirement shown is based on reduced wattage, but the real benefit appears in the decreased time required to shred to a n optimum alkali cellulose density. For the two agents shown, the cationic is the more effective in this particular application. Perhaps the most important beneficial action of treats in shredding the pressed alkali cellulose is that they improve the porosity and accessibility of the alkali cellulose crumb to carbon disulfide vapor in the subsequent xanthation reaction. This results in a more efficient utilization of the carbon disulfide charge and provides a definite economic gain, as under near-ideal conditions a given carbon disulfide usage will result in a better filtering viscose dispersion. Figure 4 shows the effect on viscose filtration (plugging value) of applied treat concentration for two Lvocd pulps, one a sulfite and the other a sulfate type cellulose. T h e agent used here represents one of the most effective nonionic type materials. An increase of filterability, as shown by this sulfate pulp, can raise a n otherwise commercially unusable pulp to a level of commercial acceptance. T h e larger gain obtained for this sulfate pulp, as compared with the sulfite, is primarily due to
a
w 50 W
Behavior in Steeping Operation In the first step of the viscose process, cellulose is steeped in caustic soda solution. T h e degree to which three typical surfactants are extracted by the caustic solution is shown in Figure 1. T h e actual loss in applied treat for the nonionic additive is less than 2070 for this initial steep, and of course it rapidly approaches zero as a slurry steep system reaches equilibrium. Loss in steep liquors is not governed entirely by solubility factors but involves mechanical
Figure 1 . Loss of applied treat to the caustic steep solution was less than 20% for the nonionicsurfactant Slurry steep: liquor to pulp ratio, 25 to 1 ; 18.570 caustic; 40' C.
+ m K W
5
25
i
z I-
E
2 g o SURFACTANT ON PULP BEFORE STEEPING - % VOL. 51, NO. 4
a
APRIL 1959
535
Figure 2. The greater the volume of clear liquid a t the bottom of the cylinders, the greater the clumping, floa,ting, and foaming and the less effective the additive Standard slurry was prepare d in Waring Blendor--type mixer
its greater initial density and fiber toughness as well as its lo\ver initial content of residual native resins. Folloiving filtration, viscose is normally deaerated a n d ripened, prior to being spun into yarn or cast into film. I n both of these steps there is no specific benefit from the additive. I t is true that some surfactants may. under borderline conditions of short cycle or excessive depth of solution, give rise to foaming during deaeration of the viscose, because of reduced surface tension. For a properly chosen treat agent and filmtype continuous deaeration sequence, however, there is no problem in this respect.
Viscose Spinning
ette oricces. I n spinning highly purified chemical cellulose without additives, encrustations around and within the spinnerette holes can build u p and become a serious problem, causing nonuniform denier, broken filaments. “fishhooks.” ‘ h o r m s . ” “slubs.“ and many other ailments, sometimes leading to shutdo\vn of the spinning position and certainlv to reduced output of top quality end products. T h e bar graph (Figure 5) compares four surface active materials with respect to their anticratering protective properties. T h e cratering index referred to is a measure of the percentage reduction in area of the spinnerette orifice using a standardized set of exaqqerated spinninqconditions especially conducive to crater formation. Measurable craterine is attained in a matter of 2 to 3 hours of spinning time. T h e reduction in area is measured by microscopic examination of the spinnerette. v
O n e of the earliest and probably still the most important role of additives in viscose operations lies in the prevention of crater formation in the tiny spinner-
Table I.
Stability of Additives
Most were stable in the steep liquor and in the spin bath
Surfactant Nonionic 1 Nonionic 2 Cationic 1 Cationic 2 Anionic 1 Anionic 2 Anionic 3
Name
Block polyoxypropylene-polyoxyethylene condensates Igepal C0630 Nonylphenol-ethylene oxide condensates Nopco 2265 Mixed diamide of ethylene triamine and long and short chain acids LPC Lauryl pyridinium chloride Nacconol NR Sodium alkylbenzene sulfonate Sodium oleate Fatty acid salt Sodium rosinate Resin acid salt
A t 50’ C . after 1 month.
536
Cheniical Ideiitity
Pluronic L64
Conversion t o corresponding acid.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Dec*onipositiona I n spin In KaOH bath None
None
None
None
Slight
None
Marked None None None
None None b b
T h e solubility and stability of the additive in the acid spin bath must also be considered in the selection of suitable anticratering agents. Table I shows that five of the six selected agents tested proved to be virtually unaffected by the acid spin bath, but there are many others on the market that d o not possess this degree of stability. Analyses T h e analvtical data presented here for nonionics 1 and 2. and cationics 1 and 2. \t ere obtained by infrared spectroscopic techniques. Absorbance val:ies of characteristic bands for known quantities of each surfactant, in suitable organic solvents. were used to prepare the necessary analytical curves. T h e substance to be analyzed. whether solid or liquid, was first thoroughlv extracted with the appropriate organic solvent. and the extracting solution was then concentrated to the desired degree to permit accurate infrared anal>sis. These analy e s were all sensitive to about 1 nig. of surfactant. Figure 6 shoms the infrared absorption spectra of the various surfactants with the peaks used for analysis denoted by asterisks. In these analyses carbon disulfide was used as the solvent for the nonionics a n d chloroform for the cationics. I n analyzing film for trace amounts of nonionic 1, a colorimetric method ( 3 )was used i n place of the infrared method. For the anionic alkyl aryl sulfonate, a well known analytical procedure was employed by which the sulfonate is titrated with a cationic alkyl pyridinium halide in a two-phase system of chloro-
8 U R F A C T A N T S IN V I S C O S E P R O C E S S I N G
0 NCNIONIC
$ .
100
*I
9 CATIONIC II I
-
1 n W IL: Lo X
0
t-
n 75 3
n
B
3
n
2 g
5c
L I P
OC 05
IO
AMOUNT
OF
APPLIED
TREAT
05
0I5
0 IO
20
.I5
AMOUNT
-%
Figure 3. Surface active treats can reduce the power requirement for shredding alkali cellulose from a dissolving Pulp
OF
AFF'LIED TREAT-%
Figure 4. Surfactant treats also enhance the ability of alkali cellulose crumb to utilize carbon disulfide in the xanthation reaction and thus create improved filterability Pulp No. 1, sulfite; pulp No. 2, sulfate
form and \\ater, using meth>lene blue as indicator ( 7 ) . Effect o n Tire Cord Properties
Additives can also influence tire cord fatigue properties (Figure 7 ) . T h e effect for the majority of additives is detrimental; ho\vever, a few agents-e.g., nonionic l-actuall!may be used effectively to increase the fatigue-life potential of rayon tire cord above untreated controls ( 2 ) . This results presumably through the ability of such agents to disperse residual undesirable native resin agglomerates a n d , in certain cases, to contribute to regeneration retardancy. T h e recent direct application of certain surfactants. particularly ethylene oxide condensates. as viscose modifiers should
also be mentioned. Acting either directly or indirectly as regeneration retardants in the spinning operation, they keep the extruded filament in a semiplastic state and thus permit more extensive application of orienting high stretch. Seireral compounds possessing this unique capacity are being used to perform key roles in high stretch processes for manufacture of the neiv Tyrex tire cords. R e m o v a l of Surfactants in Film or Yarn Washing Steps
T h e preceding discussion has dealt with the processing advantages that may I
be realized in proper use of selected surface active treats. Their value, however. would be seriously rrduced if undesirable residues v e r e to remain in the finished regenerated products Fortunately. for certain of the more effective agents no\\ being recommended foi use as viscose process aids or as spinnins assistants. the residual level in yarn or film is so low as to be virtually negligible. Figure 8 shows the course of a nonionic agent entering the viscose process as a treat applied to cellulose and traces its removal from the cellulose as it is processed through the conventional steps into cellophane film. A similar path
IOC
X
w n
z -
(3 5.c
z K
G
E
0 0 -
S U R FACTANT Figure 5. Probably the most important role of additives is the prevention of cratering in spinnerette orifices Cratering index i s a measure of percentage reduction in orea of spinnerette orifice under certain conditions; amount of surfactant used was 0.1 0% based on cellulose
10
3000
2000
-
1600
1200
800
FREQUENCY (CM -I)
Figure 6. Infrared absorption spectra were prepared for the surfactants, and asterisks denote peaks used for analysis VOL. 51, NO. 4
APRIL 1959
537
TREAT ADDED TO CELLULOSE
E q
0.I
%e
1.0%
"Ot
I
-1 W 3
c3 -
E
0 ' PCILP
250
AGENT
=I
Figure 7. Although most of the additives had a detrimental effect on fatigue properties of tire cord, nonionic 1 actually increased fatigue life potential
followed by anionic 1 and cationic 1. I t is evident that the major removal of the treat occurs in the initial acid washing stages in the film finishing operation. Although there is a small loss in the steeping caustic, the major portion of the treat remains with the cellulose through the casting stage and is then removed in early washing stages. I n many current uses for regenerated cellulose products it matters little just how low the level of treat residue actually is in the finished product. However, for film intended for food wrap purposes it is necessary to show beyond any reasonable doubt that the residual treat level is of such a nature, or existent in such low amount, as to leave no potential toxicity problem. T o ensure that this is actually the case, cellulose was treated with the normal amount of O . l % , as well as 10 and 20 times this amount, of one nonionic which has proved to be a spectacularly effective cellulose treat agent. I t was converted into film by the conventional viscose process. These films were then analyzed for their content of treat agent. For analysis, 50-gram portions of the film were extracted with water as well as a group of solvents recommended by the United States Food and Drug -4dministration (Table 11). T h e extractions were carried out a t 25' C. for a
Table II. These Solvents W e r e Recommended b y U. S. Food and Drug Administration for Film Extraction Tests d q . Soln. Concn., SZ
538
I
I
VISCOSE
REGENERATED FILM
WAmEO FILM
FILM PROCESSING STAGE
S UR FACTANT
NaCl NaHC03 CzHsC0 OH Lactic acid Sugar solution Vegetable oil
I
ALKALI CELLULOSE
3 3 3 3 20 100 (pure)
Figure 8. A nonionic agent which enters the viscose process as a treat has been completely removed b y the time cellophane film is produced
period of 72 hours on I-inch-Lvide ribbons of the film. The extracts were concentrated and analyzed by a colorimetric method based on the procedure described for polyalkylene ethers by Shaffer and Critchfield ( 3 ) . The sensitivity of such techniques is excellent, as the lomest detectable concentration of the treat in aqueous solution was determined to be 0.5 p.p.m.; moreover, by preconcentration of the water extract, detectability could be reduced to 0.2 p.p.m. of surfactant on the film. Identification can be positively made through use of infrared spectra as illustrated in Figure 6. T h e various solvents were used in extracting the treat agent from film control samples prepared to contain 10 p.p.m. of the treat, on a moisture free basis. hnalysis of the concentrated extracts demonstrated that water quantitatively extracted the treat agent from the film, whereas some of the other solvents did not. Furthermore the lvater extracts could be more highly concentrated than those of the other solvents, thus permitting greater sensitivity of the method. Hence water was selected as the most suitable solvent for isolating and concentrating any trace residues of this agent in film products. The results of the analyses obtained on water extracts of the test films are given in Table 111. At even 10 times the normal addition of a typically useful treat in pulp raw material, the amount retained i n the final film product is not detectable-i.e., to the limit of 0.2 p.p.m. This establishes beyond any reasonable doubt that a t normal usage, residues of this surfactant in the final film are so low as to assure no toxicity danger, even if the material itself were toxic-and it is not. Thus it is concluded that this surfactant may be used freely in the viscose process even when the end product is film intended for food wrap.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Table Ill. At Even 10 Times Normal Addition Surfactant Was Not Detectable in Finished Film Treat Addition t o Pulp, %
a
Found in Film, P.P.M.
0 . 1 (normal level) 05 0 . 5 ( 5 X normal) Oa 1.0 (10 X normal) Oa 2 . 0 (20 X normal) 0.5 Limit of detection -0.2 p,p.m.
literature Cited (1) House, R., Darragh, J. L., Anal. Chem. 26, 1492 (1954). (2) Mitchell, R. L. (to Rayonier Inc.), U. S. Patent 2,805,169 (Sept. 3, 1957). (3) Shaffer, C., Critchfield, F. H., Anal. Chem. 19, 32-4 (1947).
RECEIVED for review June 18, 1958 . ~ C C E P T E D December 8, 1958 Division of Cellulose Chemistry, 132nd Meeting, ACS, New York, N. Y . , September 1957.
Correction Multicomponent Distillat ion Calculation on the IBM 704 I n the article on "Multicomponent Distillation Calculation on the IB,M 704'' [John Greenstadt, Yonathan Bard, and Burt Morse, IND.ENG.CHEM.50, 1644 (1958)l Equation 3 should have an equals sign inserted before the last portion -G,(S). Equation 8 should have a n equals sign inserted before the last portion, --Fn(q). O n page 1645, the last portion of Equation 18 following the plus sign should read: XdSi
