CROSSLINKING CELLULOSE ACETATE IN SOLUTION WITH CERTAIN METAL CHELATING AGENTS J O H N E.
K I E F E R AND GEORGE P. T O U E Y
Research Laboratories, Tennessee Eastman Co.. Diusion of Eastman Kodak Co., Kingsport, Tenn.
Unique crosslinking agents for increasing the viscosity of cellulose acetate solutions were investigated. The purpose of modifying the solutions was to facilitate the spinning of extremely fine denier fibers. Several aluminum, titanium, and zirconium coordination complexes were prepared. Low concentrations of the coordination complexes, or chelates, had a pronounced effect on the viscosity of the solutions, but the physical properties of the cellulose acetate remained unchanged. The crosslinking agents included the aluminum, titanium, and zirconium chelates of dihydroxy, diketo, and hydroxy keto compounds, and keto carboxylic acid esters. One of these, the titanium chelate of ethyl acetoacetate, was studied in detail as a crosslinking agent for cellulose acetate solutions. Some of the variables encountered were investigated. The modified solutions of cellulose aceiate were stable to heat and storage. They were spun into fibers of 0.75 to 1 .O denier per filament.
possibility of modifying the viscosity of cellulose acetate Tsolutions . bv means of crosslinking agents was studied to HE
develop spinning solutions M hich would produce fibers of extremely fine denier. \l’hen cellulose acetate is spun from acetone by the usual dry spinning process, the denier of the fiber is dependent on the size of the spinneret orifice, the spinning draft, and the solids concentration of the spinning solution. The relationship of these factors to the fiber denier is illustrated by the following equation : Denier filament = K(dope density) (orifice diam.)*(solids concn., 7,) spinning draft
1; is a constant, and spinning draft is defined as the linear speed of yarn take-up divided by the linear extrusion speed of the spinning solution. Cellulose acetate cannot be drafted extensively under normal spinning conditions, and therefore this variable is not very useful in controlling fiber size. T h e orifice diameter is the variable ordinarily used to control denier size ; however, practical considerations put a lower limit on the size of orifice which can be used successfully. Since it is not desirable to change the spinning solvent, the dope density cannot be varied to control the denier size. Lowering the dope solids concentration appears to be the most effective method for spinning fine denier fibers. However, when solutions of low solids concentration are spun, the solution viscosity is too low, and the extruded solution cannot be pulled into a fiber. This investigation was limited to the use of crosslinking agents as a means of modifying the viscosity of a cellulose acetate solution of low solids concentration. A variety of crosslinking agents was tested for this purpose. T h e most effective crosslinking agents were organic chelates of aluminum, titanium, and zirconium. One of these products, a titanium chelate of ethyl acetoacetate (EAAT). was studied in some detail. Solutions containing this additive were spun and the properties of the fibers measured.
Experimental
A simple screening test was used to determine the effect of crosslinking agents on the viscosity of a cellulose acetate solution. Cellulose acetate with a n acetyl content of approximately 40% was dissolved in acetone. The solution contained 1.5% water, which was included in this formula because it is usually present in cellulose acetate spinning dopes. T h e solution, which contained 20% solids, was divided into 400-gram portions. One portion was diluted Jvith 25 grams of acetone and used as the control. T o each of the remaining 400-gram portions was added 4 grams of the crosslinking agent being tested dissolved in 25 grams of acetone. Each solution was mixed for 30 minutes, and then its viscosity iras measured with a Brookfield viscometer. The following is a representative list of the crosslinking agents tested:
+
Formaldehyde 5% oxalic acid Glyoxal 5CGoxalic acid 2-Methyl-$-phenylene diisocyanate p-Bis(2,3-epoxypropoxy)benzene Isopropyl aluminum(II1) Butyl titanate(IV) 2-Ethylhexyl titanate( IV) Octadecyl titanate( 1V)
+
T h e aldehydes, diisocyanates, and diepoxy compounds had no effect on the viscosity of the solutions. I t was thought that the water in the dopes prevented the cross linking agents from reacting with the free hydroxy groups of the cellulose acetate. Therefore, the experiments were repeated with distilled acetone and dry cellulose acetate. Again, no increase in viscosity was observed Titanium esters and acylates and aluminum esters were also unsatisfactory. T h e esters decomposed when dissolved in the acetone and their corresponding oxides precipitated. When the esters were added to the cellulose acetate solutions, they reacted too rapidly, and highly crosslinked gel particles formed in the dopes. No increase in viscosity was observed. T h e titanium acylates are reported to be more stable than the esters; however, they had no effect on the viscosity of the cellulose acetate solution. These esters could probably be used as viscosity modifiers if the solutions were anhydrous, but this VOL. 4
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would not be practical, since both acetone and cellulose acetate absorb water from the atmosphere under normal humidity conditions. The following structural formulas shobv some titanium chelates which were reported to be crosslinking agents for cellulose esters. Schmidt ( 7 ) claimed that when these complexes were added to certain lacquer formulations containing a cellulose ester, no immediate viscosity change occurred ; but when the solution was cast into a film and the solvent was evaporated, the cellulose ester crosslinked, which caused the film to have a higher softening temperature. We found that when these chelates were dissolved in acetone and added to a cellulose acetate solution, the viscosity of the solution increased rapidly for 20 to 30 minutes and then no further change took place. As little as 0.2% of the chelate, based on the weight of cellulose acetate, increased the viscosity of the solution threefold. The modified solutions were smooth, contained no gel particles, and \vere easily filtered. CZH5 I I
C H I (CHz) zCHCHCHZ
I
0
/ I
‘
0.0
0.1
0.3
0.4
Figure 1. Effect of concentration of titanium chelate of ethyl acetoacetate on viscosity of cellulose acetate solutions
2 moles of the ethyl acetoacetate per mole of isopropyl titanate(1V) was used, the complex was still an effective modifier, but the crosslinking reaction was more rapid and therefore more difficult to control. The use of more than 2 moles of ethyl acetoacetate per mole of the titanium ester did not produce a more effective crosslinking agent.
OH I
I
0.2 CHELATE CONCN., %
0
0
ll
/I
CHaCCHZCOCzH5
I
T i [OCH(CH3j2 1 4
4-
It
+
CH3C=CHCOC*HS
I
OH
IJ
0
CH,C=CHCO CzH5 t
1
I/
/’
(CH3) 2CHO,Ti--OCH(CH3) //
2
f 2 (CHI) 2CHOH
I
0’
0
I/
1
CzHSOCCH=CCHa C H SC=CHCCH I
0 I
,
0 /’
,/-
(CH3),CHOITi-OCH(CH3) //
O/
/I
3
I1
z
I 0 I
CH&CH=CCH3 The titanium chelate of 2-ethyl-l,3-hexanediol was obtained from E. I. du Pont de Nemours & Co., Inc. T h e others were prepared in our laboratory. The following equation shows the reaction involved in preparing one of the chelates. Two moles of ethyl acetoacetate were mixed with 1 mole of isopropyl titanate(IV), and 2 moles of isopropyl alcohol were removed by distillation. EAAT prepared in this manner was a n amber liquid which was immiscible with water. Actually it was not necessary to remove the alcohol from the reaction mixture. When ethyl acetoacetate was mixed with the isopropyl titanate(IV), the chelate formed was an effective modifier, regardless of whether or not the alcohol was present. However, it was desirable to remove the alcohol, since, if not removed, it complicated recovery of the spinning solvent. When less than 254
l&EC PRODUCT RESEARCH A N D DEVELOPMENT
Since the titanium chelates were so effective as viscosity modifiers, the following chelates of aluminum and zirconium were prepared and evaluated. They were prepared by a method similar to that used to make the titanium chelates. For example, 1 mole of 2,4-pentanedione was mixed with 1 mole of aluminum triisopropoxide, and 1 mole of isopropyl alcohol was removed by distillation to obtain the aluminum chelate of 2,4-pentanedione. Although some of the aluminum and zirconium chelates were comparable to the titanium chelates in terms of their ability to increase the viscosity of cellulose acetate solutions, in general they had no advantage over the corresponding titanium compounds. Therefore, the remainder of the work consisted of a more thorough study of dopes modified with one type of chelating agent. EAAT, prepared from 1 mole of isopropyl titanate(1V) and 2 moles of ethyl acetoacetate, was chosen for this evaluation, since it was one of the best chelates tested. Cellulose acetate spinning dopes modified with this chelate were studied to determine the effects of: the crosslinking agent concentration on the dope viscosity, heat and storage on the crosslinked dope, temperature on the crosslinked dope, and water in the dope on the efficiency of the crosslinking agent.
CHaC=CHCOCtHr
1
I/
0 0 \Al/' (CH3)zCHO'
'OCH(CH3)z
----
CHsC=CHCCHs
!I
1
10
i
25
30
35 40 TEMPERATURE, "C.
45
50
Figure 2. Effect of temperature on viscosity of crosslinked cellulose acetate solution
CH3C=CHCOCzH5
I
ii
225 r
.o
0
\ '
(CH3)zCHO--,Zr/-OCH (CHI)2
o/' '
0
(1
CzHsOCCH =CCH 3 Figure 1 illustrates the effect of EAAT concentration on the viscosity of cellulose acetate solutions. A very small amount of the crosslinking agent added to the cellulose acetate solution produced a remarkable increase in its viscosity-for example, 0.170 of the additive, based on the weight of cellulose acetate, increased the viscosity of the system by SOY0, 0.2% increased it by 30070, and 0.3Yo increased it by 600%. The solution contained 2070 cellulose acetate with a n acetyl content of 40%. The solvent was acetone and the dope contained 1.5% water. T h e large increases in viscosity are believed to be due to the crosslinking of the cellulose acetate. One possible crosslinking reaction is :
0'
/I
0
I.
C2HSOCCH-CCHs CHaC=CHCOC*Hs
I
II
p
0,
\ ;' Cello-Ti-OCell I'
\
0'
0
II
I
+ 2 (CHa)&HOH
CzH&OCCH= CCH, Although we are not sure that this is the reaction which takes place, we know that the crosslink is permanent. For example, a crosslinked solution containing 20'30 cellulose acetate was poured onto a glass plate and the acetone was removed by evaporation. T h e inherent viscosity (measured on a 0.25Y0 solution in dichloromethane a t 28' C.) of the dried material was only 9% higher than that of the uncrosslinked starting material. However, when the dried ester was redissolved in
75
I
0
Figure 3.
1.0
WATER, %
2.0
\ 3.0
Effect of amount of water on viscosity
of cellulose acetate solutions
acetone, the viscosity of the redissolved crosslinked ester \vas 3007, higher than that of the uncrosslinked starting material. Experimental data also showed the crosslinked solutions to be stable to heat and storage, which indicates that they can be used under any of the conditions normally encountered in spinning. Crosslinked solutions were heated a t 50' C. for 2 hours, then stored for 3 months a t 30' C . without any significant change in viscosity-. I n Figure 2. the viscosity-temperature relationship of a crosslinked solution is compared with that of the unmodified solution. The solution represented by the broken line contained 207, cellulose acetate and 0.27' EAAT. based on the weight of cellulose acetate. The solid line represents a cellulose solution which contained 287, cellulose acetate. The viscosity-temperature curve for the modified solution has a greater slope than that for the unmodified solution. Therefore, when the amount of chelate required to obtain the desired viscosity increase is calculated, the temperature a t which the dope will be used must be taken into consideration. . The amount of Lvater in the modified solutions also produced very marked effects on viscosity. Solutions with varying amounts of water were modified with O.2Y0 EAAT, based on the weight of the cellulose acetate. The results are shown in Figure 3. The solutions contained 20% cellulose acetate. Water was added to the dopes, then an acetone solution of the chelate was added. I t is obvious from these data that excess water retards the reactivity of the crosslinking agent. However, when 27, water was added to a solution in which the cellulose acetate had already been crosslinked with EAAT, no significant change in viscosity \vas noted. T o determine if these crosslinked solutions could be spun by using normal spinning techniques, a typical spinning solution VOL. 4
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255
Table I.
Effects of Chelate Concentration on Fiber Properties
Tensile Projerties
EA,4T,a
Conclusions
c7 /C
0 0.1 0 2 0 25 a Concentration cellulose acetate.
finer than those obtained from the unmodified solutions. As expected, the solutions containing the loiver amounts of dissolved solids produced the finer fibers.
28 25 20
1.6 1.3
1.30
30 1 24 31 0 9 1 14 2: 15 0 7 1 22 29 of ethjil acetoacetate titanium chelate, based on
230 224 ~~
232 234 w i g h t 01
containing 287, cellulose acetate was prepared and divided into four portions. Increasing amounts of E.4AT dissolved in acetone were added to three of the solutions. Enough acetone was added to each of the modified solutions to make them all have approximately the same viscosity. The amounts of EAAT and solids present in the solutions are shown in Table I . The solutions \\ere spun under identical conditions by using a conventional acetate spinning cabinet. The data in the table indicate that the solution modifier has little or no effect on the physical properties of the fiber. However, the deniers of the fibers from the modified solutions were much
Increasing the viscosity of cellulose acetate solutions by means of certain crosslinking agents offers a promising method for spinning fine denier fibers. Several titanium, aluminum, and zirconium chelates were found to be excellent crosslinking agents for this purpose. The EA4L\ATwas studied in detail. The addition of only 0.27, of this compound. based on the Lveight of the cellulose acetate. to a spinning solution resulted in a threefold increase in viscosity. The modified solution was stable to heat and storage conditions normally encountered in spinning cellulose acetate. Yarns of very fine denier were spun from the modified solutions. Literature Cited
(1) Schmidt, F. (to Farbenfabriken Bayer, A. G . ) , U. S. Patent 2,680,108 (1954). RECEIVED for review March 19, 1965 ACCEPTEDSeptember 22, 1965 Division of Cellulose. LVood. and Fiber Chemistry, 147th Meeting, ACS, Philadelphia, Pa., April 1964.
EPOXIDIZED CELLULOSE M A R T I N E. ROWLEY AND GORDON Cellulose Technoloxy Dicision. Eastman Kodak Go.. Rochester, .V. Y .
D.
ESTERS
H I A T T
Unsaturated cellulose mixed esters were prepared, then treated with peracids to yield epoxidized cellulose esters that retained the solubility characteristics of the original esters. Conversion of the double bond to the oxirane ring ranged from 12 to 8070~the products contained 0.02 to 0.20 equivalent of oxirane oxygen per 100 grams. m-Chloroperbenzoic acid was more efficient than peracetic acid in the epoxidation of cellulose acetate crotonate. Epoxidized cellulose acetate 1 0-undecenoate showed good properties for a wood lacquer. OBJECT of this investigation was to prepare cellulose esters containing potentially reactive groups which could be activated a t the desired time by heat or a suitable catalyst. Specifically, unsaturated cellulose esters were converted to epoxides. Peras (9) has described the oxygenation of an allylcellulose with various reagents to produce derivatives containing up to about 0.1 mole of active oxygen per 100 grams of product ; these oxygenated cellulose ethers were insoluble in organic solvents. The epoxidized cellulose mixed esters described in this article were soluble in organic solvents and readily insolubilized when used as a coating material.
THE
Methods
Table I lists the unsaturated cellulose esters that were epoxidized. Peracetic Acid Epoxidation. Peracetic acid was used to convert the unsaturated esters to the epoxides by two methods. In the first method, the peracid was formed in the presence of the unsaturated cellulose ester, using hydrogen peroxide, acetic acid, and a n acidic ion exchange resin. This method is essentially that described by Greenspan and Gall ( Z ) , but 256
l&EC PRODUCT RESEARCH A N D DEVELOPMENT
\vith some modification since \ve were dealing with solid polymeric esters that required larger amounts of solvent. In the second method, known concentrations of peracetic acid in acetic acid (or mixtures of acetic acid and ethyl acetate) \\ere used. The peracid solutions were prepared in a manner similar to that described in Method I. then added to the unsaturated cellulose ester. Typical examples are cited for the tpco methods
METHOD I. To 5 grams of acetic acid and 20 grams of ethyl acetate was added 15 grams (0.04 mole of unsaturated substituent) of a cellulose butyrate 10-undecenoate containing 43.374 10-undecenoyl. After the ester had completely dissolved, 1.5 grams of Amberlite CG-120 resin (acid form, wet with a n equal weight of acetic acid) \\as added and the flask placed in a 70' C. bath. T o the continuously stirred mixture was slowly added 4 grams (0.07 mole) of 59% hydrogen peroxide (FMC Corp.). Stirring was continued for 4 hours to complete the epoxidation. The solution was diluted with acetone and filtered to remove the resin catalyst. The product \vas isolated by precipitating into distilled water, washed with a 50: 50 mixture of methanol-Lvater, then dried a t room temperature under vacuum. Analysis showed 0.2 equivalent of oxirane oxygen per 100 grams of product (about 807, conversion of the double bond).
