HERMANNJ. JANSSEN, A. MASON D ~ P R CHESTER ~, H. HAYDEL, JEUEL F. SEAL, and HENRY L. E. VIX Southern Regional Research Laboratory, New Orleans, La.
Continuous Cyanoethylation of Cotton Yarns Products are superior in breaking strength and heat resistance to those cyanoethylated by more conventional procedures
A
SERIOUS PROBLEM in the development of a process for cyanoethylation of cotton is excessive formation of byproducts resulting from reaction of the acrylonitrile reagent with water in the presence of alkaline catalysts, particularly a t elevated reaction temperatures. This side reaction probably proceeds through a n intermediate stage, ethylene cyanohydrin, which further reacts with acrylonitrile to form the end by-product, p,P'-oxydipropionitrile (77). The loss of acrylonitrile through this mechanism has been studied extensively (4, 9 ) for cyanoethylation procedures (4, 5) which employ separate units for application of catalyst to cotton and for the subsequent reaction. The reagent losses, under a wide range of processing cmditions, were reported to vary from 3 to 49 parts for each part chemically combined with the cellulose. Such excessive reagent loss is one of the principal factors to be overcome in commercialization of the process. Recent developments have included a one-step process, independently achieved by Gruber and Bikales ( 9 ) and Compton ( 4 ) ,and a vapor procedure by Compton (4) in which reagent losses were reportedly reduced to approximately a 1 to 1 ratio with reagent reacting with the cellulose. An exploratory investigation of a continuous method for the cyanoethylation of cotton yarns, based on a prototype design by Compton (3, 4) and which still further reduces by-product formation, is described here. Essentially this reduction was accomplished by removing the excess reagent from the yarn before reaction and keeping the excess at conditions that retard formation of j3-p'oxydipropionitrile.
heat transfer during cyanoethylation. The rollers of the pulley system were constructed of an acrylonitrile-resistant phenolic resin (8), to minimize friction. Additional rollers were installed to permit multiple passes of the yarn through both the reagent impregnation and reaction baths. In the diagram, the reaction vessel is rigged for doublepass operation. The final modification involved installation of a brush above the reaction vessel outlet and separation of each individual yarn before it passed through the brush to remove entangled globules of mercury. The auxiliary equipment included a separate catalyst bath, padder rolls to reduce the wet pickup of catalyst solution to the selected values, a thermostatically controlled water bath to provide hot water to heat the mercury to reaction temperatures, a multiple-point temperature recorder for process control, and a motor-driven skein winder to receive the treated yarns. Materials
Yarns spun from the Deltapine variety of cotton were used. The yarn sizes and
constructions comprised 20s/l, 7s/l, 14s/2, and 7s/3 (equivalent to 29.5, 84.4, 42.2s X 2, and 84.4s X 3 Tex, respectively), all twisted for maximum strength (4.1 twist multiplication), a 2041 oflow twist (3.5 T.M.), and a 20s/l of high twist (4.5 T.M.). Quantities of the 7s/l and 14s/2 yarns were scoured at near boiling temperatures with 2Yo sodium hydroxide solution, containing a suitable wetting agent, for 2 hours, then thoroughly washed with hot water and dried. Procedure
The cotton yarns were continuously drawn from a set of four bobbins through guide eyes installed immediately above each bobbin. They were gathered through a master guide eye and fed into a graduated glass cylinder containing 500 ml. of the catalyst solution, usually composed of 3% aqueous sodium hydroxide with 0.1% Tergitol P-28 wetting agent. The immersion period varied from 30 seconds to 5 minutes, depending upon the rate of yarn travel. The minimum 30.second period was sufficient for complete penetration of the
Apparatus
A glass reaction vessel and auxiliary processing equipment were used. The reaction vessel was similar to that recently described by Cashen: Buras, and DuPr6 ( 2 ) . Its construction integrated into one unit: reagent impregnation, removal of excess reagent, chemical reaction, and washing. Mercury was used as the medium to pad off the excess reagent and provide good
76
Glass reaction vessel and auxiliary processing equipment for continuous cyanoethylation of cotton yarns
INDUSTRIAL AND ENGINEERING CHEMISTRY
catalyst into the yarns. These catalysttreated yarns were separated by spacer rods and padded between squeeze rolls set to provide approximately 125%, by weight, of caustic solution pickup. The yarns then passed over guide rollers and down through the acrylonitrile reagent in the inner tube of the top section of the reaction vessel, The acrylonitrile reagent was maintained a t room temperature by circulation of cool water in the jacket. The yarns, now containing acrylonitrile dissolved in the absorbed catalyst solution and possibly some entrained acrylonitrile phase, were guided by the pulley system into the mercury bath. The pressure exerted by the mercury around the periphery of the entering yarns padded o f f excess reagent. The cyanoethylation reaction took place within this mercury bath, which was maintained at a preselected reaction temperature by circulation of thermostatically controlled hot water through the mercury bath jacket. The yarns, still undergoing reaction, passed over guide rollers a t the bottom of the mercury column and returned through the length of the bath. When the double-pass system was employed, the treated yarns were led through the acrylonitrile reagent and mercury cycle a second time. Before leaving the mercury, the yarns passed on the outer side of the inner glass tube and entered the jacket surrounding the reagent impregnation bath. The cool wash water circulating within this jacket was slightly acidified with acetic acid to neutralize the^ alkaline catalyst and prevent hydrolysis of the product or cleavage of cyanoethyl groups from the cellulose. The wet, cyanoethylated yarns were then directed over stainless steel rollers through a current of cool air, which quickened the drying rate, and finally wound in skeins. Adjustment of the speed control on this skein winder regulated yarn speeds throughout the processing system. The skeined yarns were analyzed for nitrogen by the Kjeldahl method and tested for breaking strength, elongation, and resistance to heat and rot.
yarns that still contained noncellulosic constituents-than with scoured yarns. These differences gradually decreased with increased temperature, although a lower maximum of substitution persisted for the scoured yarns. The effect of time of reaction, a t constant reaction temperature, on the extent of cyanoethylation was investigated for the 84.4 Tex yarn (lowest set of figures in Table I). The same low limit to the nitrogen content is taken as a further demonstration of the efficacy of mercury padding. Use of water-saturated acrylonitrile (about 3% water a t 25' C.) rather than the commercial reagent, which normally contains less than 1% of water, markedly reduced reactivity. Tests with 84.4 Tex yarn a t speeds of 3.2 inches per minute and 90' C. gave products containing only 1.4% nitrogen, compared to 2.9% nitrogen obtained from the commercial reagent. Such results were presumably related to changes in the relative concentrations of the cellulose, water, and alkali caused by the saturated reagent. The importance of the cellulose-water-alkali ratio to the rate of cyanoethylation of cellulose has been described by Weaver and others (72). Attempts to increase the reactivity by utilizing raw yarns preswollen by boiling in water were, rather surprisingly, unsuccessful-degrees of substitution were consistently 15% lower than those otherwise obtained. Extraction of catalytic constituents from the raw cotton by the hot water may be one responsible factor.
Table I.
Effect of Reaction Temperature and Reaction Time on Extent of Cyanoethylation rp Nitrogen Reaction Yarn Tested Reaction Time, in Product, Yarn Speed, (Tex Scale) Temp., O C. Inches/Min. Min. % 84.4
57 63 70 80 90
3.4 3.4 3.2 3.3 3.2
13 13 14 13.5 14
1.7 2.8 2.8 2.9 2.9
42.2s X 2
57 63 70 80 90
3.4 3.4 3.2 3.3 3.2
13 13 14 13.5 14
1.6 2.55 2.7 2.8 2.85
57 63 70 80 90
3.4 3.4 3.2 3.3 3.2
13 13 14 13.5 14
0.7 1.4 2.2 2.4 2.5
57 63 70 80 90
3.4 3.4 3.2 3.3 3.2
13 13 14 13.5 14
0.6 1.0 2.2 2.3 2.4
63 63 63 63 63
2.3 4.5 9.0 18.0 36.0
19 10 5 2.5 1.2
2.9 2.8 2.3 1.6 0.7
Results and Discussion Experiments with the single-pass procedure (Table I) show that the nitrogen content of each yarn tested approached a constant value with increasing temperature. The rather limited degree of substitution was attributed to a low pickup of acrylonitrile resulting from the low solubility of this reagent in the absorbed catalyst solution and the high effectiveness of the mercury in padding this reagent solution from the yarn prior to reaction. Cyanoethylation proceeded more rapidly with untreated cotton yarns-
As the quantity of acrylonitrile available for reaction was restricted by this mercury process, multiple passes of the yarn through the reagent and reaction chambers were employed to obtain higher nitrogen contents (Table 11). Appreciable increases in nitrogen content were achieved, but a t a reduced rate with each additional pass. The greater increment of substitution with the first pass was assumed a result of the more rapid initial reaction of the amorphous regions of the cellulose. Later tests involving triple passes were conducted at a rate of yarn travel of one yard per minute to approach practical speeds more closely. Increases in catalyst concentration and reaction temperature were required a t this high speed to attain satisfactory degrees of substitution. These data, also reported in Table 11, show that with a catalyst concentration of 5% and a reaction temperature of 110' C. (obtained by adding glycerol fo the hot water bath) the product contained 4.5% of nitrogen. Stronger catalyst concentrations were not used, to avoid carboxyethylation of the cellulose and the conjunctive loss in rot resistance. The use of hydrotropic agents to increase the solubility of acrylonitrile in aqueous sodium hydroxide and thereby increase the rate of cyanoethylation has been described by Klein, Weaver, and Webre (70). However, recent work by Bikales, Gruber, and Rapoport (7) has indicated that swelling of the cellulose by hydrotropic salts Having monovalent, heavy, highly hydrated anions is prob-
84.4
scoured
42.2s X 2
scoured
84.4
VOL. 50, NO. 1
6
JANUARY 1958
77
ably the major factor in this increased reactivity. Results of addition of 36% by weight of potassium iodide to the catalyst solution are given in Table 11. The nitrogen content of the cyanoethylated products was increased almost 30% in the 84.4Tex yarn and 35% in the 42.2 X 2 Tex. Another modification which increased reactivity involved evaporation of water from the absorbed catalyst solution before the yarn entered the reagent impregnation chamber. Evaporation of sufficient water to reduce the wet pickup
Table
II.
Effect of Multiple Passes, Catalyst Concentration, and Catalyst Composition on Extent of Cyanoethylation
Yarn Tested (Tex Scale)
Yarn Passes
84.4
42.2s X 2 84.4 42.2s X 2 42.2s X 2
Table 111.
84.4 42.2s X 2 84.4 42.2s X 2 84.4 42.2s X 2 84.4 84.4 42.2s X 2 84.4 42.2s X 2
Yarn Nitrogen Catalvst Reaction Soeed. Reaction Time, in Min. Product Conch. Temp. Inches/ % XaOH O C. Min. Per pass Total %
Single Double Triple Triple Triple
84.4
Yarn Tested (Tex Scale)
to values below the approximate 125% normally achieved by the mercury padding permitted passage of additional acrylonitrile phase into the mercury with the yarn and changed the cellulosewater-alkali ratio. Reduction of a 125% pickup of 3% sodium hydroxide solution to 65% through evaporation of water gave a nitrogen content of 5.3% in 84.4 Tex raw yarn at 73' C. reaction temperature, 3 inches per minute yarn travel, and single-pass operation. Further evaporation to a reduced pickup of only 20% lowered the reactivity.
3
Triple
4 5
63 63 63 63 63 63
Triple Single Single Single Single Triple Triple
5 3 3 4 36% KI 3 3 36% KI 3 3 4 36% KI
110 90 90 90 90 90 90
3
3 3
+
9.0 9.0 9.0 36 36 36 36 36 36 36 36 36 36
5 5
5 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2
5 10 15 3.6 3.6 3.6 3.6 1.2 1.2 1.2 1.2 3.6 3.6
2.3 3.5 4.5 0.7 1.3 2.0 4.5 0.7 0.9 0.7 0.95 1.8 2.4
Effect of Combining Catalyst and Reagent Baths on Extent of Cyanoethylation Yarn Nitrogen Reaction Speed, Reaction in Temp., Inches/ Time, Product, Composition of Bath C. Min. kfin. % Immiscible layers, 75 vol. % of 90 3.4 13 1.1 acrylonitrile above 25% of 3% 90 3.4 13 1.1 NaOH s o h Immiscible layers, 80 vol. % of acrylonitrile above 20% of 3% NaOH s o h . Immiscible layers, 90 vol. % of acrylonitrile above 10% of 3% NaOH s o h . Emulsion of 857, of acrylonitrile with 15% of 37, NaOH s o h Acrylonitrile saturated with 3% NaOH s o h .
90 90
3.4 3.4
13 13
1.2 1.2
90 90
3.4 3.4
13 13
1.25 1.3
90
3.2
14
0.95
80 SO 100 100
4.0 4.0
11 11 11 11
0.15 0.15 0.15 0.15
4.0
4.0
Table IV.
Acrylonitrile Reagent losses during Mercury Bath Cyanoethylation Unreacted By-product Formation d4cry10Processing Conditions" In impregnitrile Total (84.4 Tex Cotton Yarn) Nitfogen nation In Leaving Reagent Reaction Rate. in chamber mercurv Mercurv Losses temp., inches/ product, (Am (Acn (Acn (Am Pass NaOH O C. min. yo ratio)b ratio)* Ratio)b Ratio)* Single Triple SingleC TripleC
3 5 3 5
63 73 73 93
3 36 3 36
2.7 2.35 5.3 4.85
Separate catalyst bath.
0.06 0.04 0.03 0.02
0.23 0.26 0.21 0.28
* Ratio of acrylonitrile lost t o acrylonitrile reacted with cellulose. 125% pickup evaporated to 65%.
78
INDUSTRIAL AND ENGINEERING CHEMISTRY
0.93 0.26 0.75 0.21
1.22 0.56 0.99 0.51
The effect of yarn size and yarn construction on the extent of cyanoethylation was studied. Treatment of 29.5, 84.4,or 42.2s X 2 Tex raw cotton yarns at 70' C. and 3.2 inches per minute yarn travel revealed that each yarr: contained 2.7% nitrogen after a single pass and 4.4% after a triple pass through the reaction system. r\-itrogen contents were slightly lower, 2.1 and 4.15%, respectively, for similar treatment of 84.4s X 3 Tex yarn. Changes in the twist multiplication of 29.5Tex yarn between the limits of 3.5 and 4.5 had no significant effect on degree of substitution. Experiments were then performed without a separate catalyst bath by direct addition of 37, sodium hydroxide solution to the acrylonitrile reagent in the impregnation chamber. Immiscible liquid layers resulted, the less dense acrylonitrile reagent forming the upper layer. The extent of cyanoethylation with this method of processing (Table 111) was of the same order of rnagnitude as those previously obtained with saturated acrylonitrile and the separate catalyst bath. Increasing the proportion of reagent to catalyst solution through the ranges of 75%,1/25%, 80%/'20%, and 9O%/lO%, by volume, slightly increased reactivity. However, emulsification of a 85%/'15% mixture by vigorous agitation with nitrogen decreased reactivity below that achieved with separate layers. Preliminary tests with air as the emulsifying agent quickly oxidized and/or polymerized the reagent and thickened the liquid mixture. The final experiment with a combined bath utilized acrylonitrile, saturated with the catalyst solution, as reagent. One hundred milliliters of acrylonitrile and 10 ml. of 3% sodium hydroxide solu. tion were thoroughly shaken together at 25' C. and allokved to separate into layers. The saturated acrylonitrile layer was drawn off and used in the test, Analysis of the treated yarns showed only 0.15% nitrogen. Subsequent titrations of the two layers with methyl red indicator revealed that only 5.3% of the dissolved alkali in the caustic solution had penetrated the acrylonitrile during preparation of the test reagent. The low degree of substitution is attributed to this relative inability of the alkali to penetrate the acrylonitrile. Reagent Losses during Process. Efficiency of utilization of the available reagent was evaluated by determining by-product formation and unreacted reagent leaving the system under four different processing conditions selected for greatest reactivity. Results of these experiments, which differentiate the losses according to their points of occurrence in the process, appear in Table IV. By-product formation in the impregnation chamber was determined by infrared analysis (7) of samples taken at the
CELLULOSE FIBERS wash by unreacted reagent. The presence of alkali-catalyzed polyacrylonitrile in the effluent yarn was generally discounted, as no appreciable yellow coloration developed in either the wash water or the acrylonitrile. The reagent loss to by-product formation in the reaction area approximated one fourth of that reacting with the cellulose. The loss of unreacted reagent, determined by the difference between the total nitrogen extracted from the effluent yarn and that attributed to by-product formation, was materially reduced by multiple-pass processing. Under these conditions the yarn, after each pass, merely returned the unreacted reagent to the impregnation chamber, with the exception of the final pass, which entered the wash water. The total reagent loss with triple-pass processing amounted to but one part for each two parts combined with the cyanoethylated product (Table IV). This low loss was achieved without the aid of apparatus for reagent recovery. The only other probable source of reagent loss in the mercury process should be evaporation of acrylonitrile from the system. This is dependent upon the equipment design and, in this case, was minimized by constricting the opening through which the yarns entered the reaction vessel. Physical Properties of Products. Cyanoethylated raw cotton yarns of 29.5, 84.4, and 42.2s X 2 Tex construction, at nitrogen levels of 2.6 and 4.5%, and their untreated controls were tested for breaking strength, elongation at break, heat resistance, and rot resistance (Table V). The improvement in breaking strength probably reflects the high
conclusion of each run and dried before testing, to avoid damaging the rock salt infrared cells. Measurements of ethylene cyanohydrin and P,P’-oxydipropionitrile content by this procedure are The very small loss accurate to &2%. of reagent to by-products on contact with the catalyst-treated yarn in the impregnation chamber was presumed a consequence of the circulation of cool wash water through the chamber jacket, which maintained the reagent at or below 25’ C. The efficiency of this cooling mechanism was indicated by measurement of reagent temperatures at points immediately above the hot mercury-acrylonitrile interface with ironconstantan thermocouples. A maximum temperature of 28’ C., only 3’ higher than the bulk of the reagent, was recorded. This low maximum probably reflected the movement of convection currents across the cool jacket wall. The sum of by-products and unreacted reagent entering the acidified wash water in the impregnation jacket was measured by nitrogen determination in a n aliquot of this wash and a n additional wash employed to assure complete extraction of these constituents; less than 2% of the total nitrogen was found in the second wash. The fraction of byproducts represented in the total and formed within the mercury bath during cyanoethylation was measured with the infrared spectrophotometer, by replacing the wash water in the jacket with acidified, fresh acrylonitrile, using this solution to extract a portion of the unwashed, effluent yarn and then testing aliquot samples for by-product formation. The values reported in Table IV were corrected for dilution of the acrylonitrile
Table V.
Physical Properties of Yarns Cyanoethylated in Mercury Bath
In Water Bath at 60’ C. N in Untreated Control Yarns In Mercury Bath by Daul Method (6) Product, 29.5 84.4 42.2s X 29.5 84.4 42.2s X 29.5 84.4 42.2s X Test 70 Tex Tex 2 Tex Tex Tex 2 Tex Tex Tex 2Tex
Breaking strength, grams per Tex 0.0 2.6 4.5
13.0
0.0 2.6 4.5
7.8
... ...
16.6
... ...
17.2
...
...
14.6 15.4
17.4 17.8
18.5 18.7
11.9 11.7
16.9 17.4
16.9 16.5
8.7 8.8
8.3 10.1
11.5 12.8
11.3 13.5
Elongation at break, %
... ...
10.6
...
...
9.0
...
...
5.8 5.5
9.4 7.9
7
...
...
11
... ...
11
... ...
34 51
46 58
56 60
27 47
24 44
24 46
Rot resistance, exposed 6 weeks t o soil burial, % of original strength retained 0.0
Failed
2.6 4.5
...
...
Failed
... ...
Failed
....
*.
44 101
77 97
80 98
46 97
83 106
Acknowledgment
The authors wish to thank Elsie F. DuPrC and Julian F. Jurgens of the Analytical, Physical Chemistry, and Physics Section for the infrared analyses and nitrogen determinations, respectively. literature Cited (1) Bikales, N. M., Gruber, A. H., Rapoport, L., IND. ENC. CHEM. 50, 87-90 (1958). (2) Cashen, P A ; , Buras, E. M., DuPrt, A. M., Textile Research J . 27, No. 5, 390 (1957). (3) Compton, J., Jones, C. P. (to Institute of Textile Technology), U. S. Patent 2,786,735 (March 26,1957). f4) Comuton. J.. Martin. W. H.. Word. B. ‘H,,‘Jr.; Barber; R. P.,’ Textile Research J . 26, 47 (1956). (5) Compton, J., Martin, W. H., Word, B. H., Jr., Thompson, D. D., Textile Znds. 117, No. IO, 138A (1953). f6) Daul. G. C.. Reinhardt. R. M.. R&d, a. D.,’ Textile Research J. 25; No. 3, 246 (1955). (7) DuPrt, E. F., Armstrong, A. C., Klein, E., O’Connor, R. T., Anal. Chem. 27, 1878 (1955). (8) Greathouse, L. H., Haydel, C. H., Janssen, H. J., IND.ENC.CHEM. 47, 187 (1955). (9) Gruber, A. H., Bikales, N. M., Textile Research J . 26, 67 (1956). (10) Klein, E., Weaver, J. W., Webre, B. G., submitted to IND. ENG. CHEM.,Chem. Eng. Data Ser., Vol. 2, No. 1, p. 27 (1957). (11) MacGregor, J. H., Pugh, C., J . SOC.Dyers Colourists 67, 74 (1951). (12) Weaver,. J. W., Klein, .E., Webre, B. G., DuPr6, E. F., Textile Research J . 26, 518 (1956). \
I
.,
RECEIVED for review March 18, 1957 ACCEPTED November 22, 1957
Heat resistance, exposed 7 days at 160’ C., % of original strength retained 0.0 2.6 4.5
degree of tension maintained in the yarns during the mercury bath treatment to overcome the friction developed a t various points. As a further consequence of this tension, the elongation a t break was reduced. Surprisingly, the mercury bath process resulted in significantly greater resistance of the treated yarns to heat degradation, particularly a t the 2.6% nitrogen level. This may reflect increased product uniformity resulting from a rapid removal of the exothermic heat of reaction by the mercury. No material differences between yarns treated by this method and that of Daul were observed in resistance to rot.
76 101
Division of Cellulose Chemistry, Symposium on New Chemically Modified Cellulosic Fibers, 131st Meeting, ACS, Miami, Fla., April 1957. Use of trade names is not to be interpreted as an endorsement of the Department of Agriculture of these products over similar products of other manufacturers. VOL. 50, NO. 1
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