CELLULOSIC FIBERS
I
ROBERT F. SCHWENKER, Jr., and EUGENE PACSU Textile Research Institute, Princeton, N. J.
Chemically Modifying Cellulose for Flame Resistance New vehicles have been de-
vised for making fabrics fire-resistant-two and a method for introducing bromine and other halogens into carbohydrate molecules
F A B R I C S OF COTTON and ofviscose rayon have been modified in a three-step themic-1 process to yield cellulose derivatives which have good flame and glow resistance and still maintain their original identity as useful textile materials. Flame resistance was imparted by esterifying with sulfonyl halide certain hydroxyl groups present in cellulose and partially replacing with halogen the sulfonyloxy groups thus formed. Glow resistance was obtained by introducing phosphorus-containing groups. At elevated temperatures, cellulose decomposes into highly volatile gases, a carbonaceous residue or char, and a tarry distillate. Water is also a major product. The tars, representing products volatile and flammable at the ternperature of pyrolysis, are held responsible for flammability of cellulosic materials. Almost three years ago, when this study of pyrolytic degradation of cellulose was begun, as an attack on the larger problem of flame and glow resistance of cellulosic materials, a mechanistic theory for decomposition of cellulose a t high temperatures had just been proposed by a group at the University of Rhode Island (70). The theory suggests that the proximal cause of the cellulose polymer's flammability is decompo$ition under continued high thermal stress of an intermediate, ]evoglucosan, to yield flammable prodUCtS. This hypothesis further implies that prevention of levoglucosan formation by chemical means could decrease flammability of the resultant cellulose derivative. Results of early work (72) supported these views as well as the levoglucosan theory for pyrolytic degradation of cellulose.
Experimental An unmodified cellulose, cotton oxford (6 ounces per square yard), and an oxidized cellulose, wherein 40 to 47% of the primary alcohol groups had been oxidized to carboxyl groups, were py-
rolyzed in air at 350' C. The tarry distillates (pyrolyzates), were analyzed quantitatively for levoglucosan by a previously described method (72). Methanesulfonyl (mesyl) chloride, an Eastman Kodak Co. prod-uct, was used to partially esterify the celluloses. This process was successfully carried out on cotton linters, cotton fabrics ranging from 4.6 to 9 ounces per square yard, and viscose rayon challis of about 3.6 ounces. The cotton fabrics were sheeting, Oxford, and having weights Of 4.6! 6, and Ounces per square yard, respectively* The cotton samples were first swollen to facilitate mesylation by a 15-minute slack mercerization at room temperature in *'% 'Odium hydroxide The samples w'?re washed free of excess and given a weak acid sour and washed again until the washings were neutral to litmus. Excess water was then removed, and the were suspended in pyridine to replace as much Of the remaining moisture as possible. Initially an anhydrous system for the reaction was 'Ought because, with amounts Of water present, the reagent react preferentially with more readily available hydroxy1 groups in the water molecule instead of those in the cellulose. However, it was later found that a amount Of water was The viscose rayon required no pretreatment except a out foll~wed by rep1acement Of water by suspension in pyridine. Samples were methanesulfonylated (mesylated) either by suspending in fresh pyridine and then adding mesyl Or by placing in a previously Of mesyl chloride in prepared pyridine* Reaction time, temperature, and mole ratio of mesyl chloride to cellulosewere varied. The is exothermic, causing a temperature rise Of l o o .' Or more* A white precipitate, thought to be pyridine hydrochloride, often forms. A second esterification using diethyl chlorophosphate (Victor Chemical Works), was carried out in a pyridine medium according to procedures used for mesylation. Also, mesylated cotton fabric was suspended in a 20% aqueous solution of sodium halide. Solid barium carbonate was added, and the mixture was heated under reflux on a steam bath for 4 to 5 hours or under pressure of about 20
pounds per square inch for 15 to 30 minutes. Samples were removed, washed, and dried. Quantitative data for sulfur, phosphorus, and halogens were obtained from commercial microanalytical laboratories. Qualitative analyses were made for sulfur and halogens according to standard procedures outlined in Shriner and Fuson (73). The match test, also called the strip flame test, is similar to that described by Reid and others (77). Strips of cloth '/4 to '/2 inch wide and 10 inches long were suspended vertically in a draft-free area and their lower ends ignited with a match. If flame propagation ceased within the bottom 1 inch, a rating of excellent was given. Ratings less than excellent were made according to the previously described method (77). The vertical flame test, Method 5902 of Federal Specifications CCC-T-1916, May 15, 1951, was used. Natural gas having a B.t.u. content of 1035 was used instead of the usual 540-B.t.u. synthetic gas mixture.
Results and Discussion Pyrolysis. For five determinations, the unmodified cellulose pyrolyzate contained an average of 12.5% of levoglucosan whereas the oxidized cellulose pyrolyzate contained 4.9'%. Theoretically, oxidation of CHzOH a t the 6 position ( 6 OH) to COOH should render those glucose residues affected incapable of forming the P-glucosan intermediate. Therefore, the oxidized cellulose should show a marked decrease in levoglucosan production with the pyrolyzate containing 5.0 to 5.8% of the compound, based on the results obtained for the unmodified cellulose. Two such materials should show important differences in burning behavior, and this was true. Unmodified cotton flamed vigorously and quickly produced a small quantity of char that was completely reduced by afterglow to an ash residue. By contrast, the oxidized cellulose burned in a desultory manner leaving a bulky char with practically no afterglow, This marked improvement seems related to the fact that for oxidized (modified) cellulose, eliminating the 6 OH by oxidation had prevented formation of levoglucosan; thus, production of flammable decomposition products was materially diminished. VOL. 50, NO. 1
JANUARY 1958
91
This certainly establishes the first step in the complex mechanism of thermal degradation of cellulose as an extensive depolymerization to form levoglucosan by scission of the 1,4-glycosidic linkages in the polymer chain accompanied by rearrangement of the chain fragments to yield the levoglucosan intermediate. A recent Russian work (7) on thermal degradation of cotton cellulose in vacuum has provided additional support for this mechanism. These workers concluded that splitting of the 1,4-glycosidic linkage with isomerization to levoglucosan is the main reaction path and that hydrolysis, oxidation, and dehydration are secondary effects, The present work led to the working hypothesis that suitable chemical modification of the primary alcohol group at the 6 carbon of the glucose anhydride unit of the cellulose chain prevents formation of levoglucosan in those glucose residues which were modified; thus, decreased flammability and improved glow resistance result. Introducing the appropriate group should enable subsequent introduction into the cellulose molecule of certain known flame-retardant elements such as bromine via a replacement mechanism, Selection of suitable modifying agents that would block the primary alcoholic function of the glucose anhydride unit posed many problems, some which are inherent in cellulose research-e.g., the heterogeneous nature of reactions carried out on fibers, effect of modification of the mechanical properties of the fiber assembly, and obtaining a modifying agent selective for the primary hydroxyl group. A modifying agent was sought having preferential reaction with the 6 OH, and low molecular weight, preferably without a benzene nucleus. Also, this agent should form a group replaceable by halogen, produce a modification stable over a reasonable p H range, and prevent formation of levoglucosan. On this basis mesyl chloride was selected, Esterification at the 6 position using a sulfonyl halide should effectively block formation of levoglucosan.
Table I.
Mesylation and Flame Tests for Cotton Cellulose (Room temp.; mole ratio of reagent to sample, 6: I)
Reaction, hr.
Sample Cotton linters
44 4SG 48 15 8 4
Cotton oxford
a
21.7 16.0
the glycosidic oxygen atom at carbon 1. For cellulose (11), labile hydrogen on the primary alcohol group should be readily released to allow subsequent formation of levoglucosan. On the other hand, the sulfonyloxy group may reddily be replaced by halide ions such as iodide. Mesylation of Cellulose. Preferential esterification of the primary hydroxyl group has been observed as a result of the sulfonylation of carbohydrate derivatives having both primary and secondary hydroxyl groups (8). Compton ( 2 ) found that tosylation, a reaction analogous to mesylation, of P-methyl-nglucoside in pyridine solution followed by acetylation yielded 6-tosyl triacetyl&methyl-D-glucoside, Helferich and Gnuchtel (4) reported mesylation as selective for the primary alcohol group. Selective tosylation and mesylation of sugars with reducing groups have also been reported (75). The reaction of mesyl chloride with cellulose to yield mesyl cellulose was described by Wolfrom and others (77) for cotton linters. Initially, the extent of reaction was estimated by weight change. If it is assumed that the sample is 100% cellulose and that 100% selectivity for 6 OH obtains, then the theoretical maximum weight increase is 48.2%. Such a sample would contain 13.3% sulfur. In these reactions it is believed
r
@T3 I n
I
1z
Sulfonic esters (I) usually do not split between the sulfur-oxygen bond,
m
;
m
t Cellulara
CH Kesyl
the carbdn-oxygen bond of the alcohol component, thereby producing a negatively charged sulfonyloxy group,
e
-OSO&,
92
which cannot react with
INDUSTRIAL AND ENGINEERING CHEMISTRY
1
1
'/a '/a
7.2
a . 0
1/2 1/2
b b
...
primary alcohol group in the glucose anhydride unit of cellulose to yield a mesyl cellulose. Temperatures referred to throughout this discussion are those of the reaction mixtures just prior to the introduction of the sample. Table I shows the effect of mole ratio and reaction time for cotton linters which was appreciably more reactive than cotton fabric. All fabric samples appeared to have been tenderized. Modified linters proved quite flame and glow resistant but the fabric samples did not (Table I), Mesylation per se was not sufficient as a terminal treatment for flame resistance and was consequently relegated to an intermediate role. Improvements in this step were mandatory to avoid deleterious effects on mechanical properties of the fabrics; also, a material reduction in reaction time was required. By increasing temperature of the reaction bath, a satisfactory level of mesylation was obtained at greatly reduced reaction time (Table 11). Also, the mole ratio could be safely reduced to 3 to 1. Reaction times of 5 to 10 minutes were adequate to form replaceable mesyloxy groups at position 6, Fibers teased from the modified fabrics as well as the fabrics themselves were not appreciably tenderized and showed no loss in tensile strength.
170 75 30 10 5
I. +
but scission involves
'/a l/4 '/1
a . .
5
I
-C-O-(-SO&
16.4 10.6 10.9 9.6
Table II. Mesylation Levels (Mole ratio of 3 : 1) Reaction, Temp., Min. C. Wt. Incr., YO Cotton Oxford CH3
b
Flame Test, Char Length, In. Horizontal Match test ~
%
S!
* Burned entirelength.
CHZO--+?,
OH
I
60.4 25.3 34.0 22.5
Mole ratio of reagent to sample, 2 : 1.
00 cn2jOSOeR
Mesvlation Data Wt. incr., %
Pyrid ne Hydrochloride
CH20H
Cellulare
that first, mesyl chloride (I) reacts with pyridine (11) to form a pyridinium complex (111) which then reacts preferentially with labile hydrogen of the
47
10.4
57
22.0
56 65 63 68 60
12.3 9.0 9.0 13.9 0.9
Viscose Rayon 60 15 6
5 6 5
65 60 63 63 63 60
25.4 15.2 9.0
9.7 9.1 8.3
CELLULOSIC FIBERS A mole ratio of 3 to 1 is almost as effective as 6 to 1. Treatment time of 5 minutes is sufficient but 1 to 2 minutes, even a t optimum temperature conditions, is inadequate (Table 111). Preheating the reaction solution to temperatures in excess of 70' C. usually results in decreased mesylation until a t 100' C. practically no reaction occurs a t all. At lower temperatures the solution is quiescent, even during reaction, with perhaps some gentle bubbling but a t higher temperatures it boils vigorously and temperature rises to more than 110' C. seem to destroy the reagent. Satisfactory mesylation of cotton requires prior swelling of the cellulose fiber. This was done by a 15-minute pretreatment with 2070 sodium hydroxide solution which is in effect a prolonged, slack mercerization process. Subsequent drying largely cancels the effect of this mercerization which opens the fiber structure to facilitate mesylation. Therefore, the wet state had to be maintained until the mesylation was completed. Commercially, fibers are usually both mercerized and dried under tension; therefore, much of the fiber change should be preserved. The effect of commercial mercerization and other pretreatment conditions on mesylation of cotton fabric was studied (Table IV). Desized and scoured sheeting, 64 X 64, and greige oxford, 80 X 80 (sample F), was used. For the sheeting, sample M was bleached and mercerized for 30 seconds in sodium hydroxide, 52' Twaddle in a commercial process, Sample NM was not mercerized. Three types of pretreatmrnt were used. The first (I) was slack mercerization for 15 minutes in 20% sodium hydroxide solution followed by 5-minute souring in dilute acetic acid, washing free of acid, removing water, and finally giving a pyridine soak. The second (11) was wetting out with water, removing excess water, and following with a pyridine soak. The third (111) was only a pyridine soak. Also, samples having no prior treatment (IV) were mesylated. Samples were placed in solutions of mesyl chloride in pyridine that had been heated to temperatures ranging from 45' to 67' C. A mesyl chloridecellulose mole ratio of 3.25 to 1 was used throughout and reaction time was 30 minutes. Commercial mercerization facilitates mesylation somewhat but further mercerization is still beneficial. Also, wetting out is a prerequisite. Effect of temperature is shown here as well as in earlier results (Table 11) and the data suggest a critical initial temperature range having an upper limit of about 65' C.
Mesyl6-HaloceUuloses. Because mesylation failed to provide good flame and glow resistance, further modification by introducing flame retardants was tried. Simmons and Wolfhard (74) found that when bromine gas was injected into a mixture of flaming gases, the flame was extinguished. Also many of the successful flame-retardant finishes have bromine as a constituent. Therefore, introduction of a halogen, preferably bromine, through a replacement mechanism was tried. Tosylation of cellulose with p-toluenesulfonyl chloride in pyridine solution (7, 6) is directly analogous to mesylation of cellulose. Oldham and Rutherford (9) showed that when tosylated D-glucose derivatives are heated with sodium iodide in an acetone solution, sodium p-toluenesulfonate is produced almost quantitatively, and iodine replaces the tosyloxy group a t position 6. The results of their work have been formulated into a set of principles called Oldham and Rutherford's rule (76) which was subsequently extended to mesyl derivatives of D-glucose (4). Cramer and Purves (3) introduced iodine into the cellulose molecule using a n acetone solution of tosyl cellulose acetate to yield a 6-iodotosyl cellulose acetate. Mesyl iodocellulose acetate was prepared by Wolfrom (77) by heating mesyl cellulose acetate and sodium iodide in acetonylacetone solution. I t therefore appeared reasonable to attempt to replace the methanesulfonate
glucoside with potassium fluoride in methanol. No method appears to have been reported in the literature for the replacement by bromine of tosyloxy (-OSO~-~-CH8) or mesyloxy (-0S02CHs) groups in their carbohydrate derivatives. Moreover, no methods for replacement by halogens in similar reactions involving heterogeneous systems have so far been used. Little is known about iodine as a flame retardant and its use seemed unattractive economically, whereas bromine is widely
Table 111.
(Effect of time, temperature, and mole ratio) Wt. Mole Soln. Time, Ratio Temp., C. Min. Incr., % 3.25:l 3.25:l 3.25:l 3.25:l 3:l 3:l 6:l 9: 1 3:l 6: 1 9:l
.
45 65 95 64 62 68 60 60 60 64 63
30
Temp., O
c.
1 11 15 5 5 5 1.2 1.1 1.2
Wt. Incr., %
Pretreat. Sample I M
45
I1
60
10.5 8.9 8.4 6.3 14.2 10.4 9.4 3.8 4.1 3.3 9.7 6.3 6.2 3.6 5.2 3.9
NM M NM M NM
I1
ion (OSO&H8) in mesyl cellulose with iodide ion and other halide ions as well, However, chemical literature, although replete with a variety of halogenation studies in homogeneous systems, revealed that introduction in a carbohydrate molecule of halogen by an exchange mechanism a t the carbon atom of a primary alcohol group has been largely restricted to iodination. In 1941, Helferich and Gnuchtel ( 5 ) prepared a 6-fluoro-2, 3, 4-trimesyl methyl glucoside by heating tetramesyl methyl
F
IV
M NM
F
I1
67
M NM
F
I11
M NM
F
Sulfur and Halogen Content of Mesyl Bromo and lodo Derivatives"
Iodocellulose S,%
Fabric Cottonoxford
Sateen
14.2 9.0 0.4 8.5 11.8 13.9 15 24.5 0.9 0.9 2.1
10
Table IV. Effect of Pretreatment and Temperature on Mesylation
e
Table V.
Mesylation of Cotton Oxford
Bromocellulose Calcd. wt. incr., % 9,% Br, % 16.6 9.7 14.6 15.7 19.5 14.9 17.3 13.1
4.28 2.53 4.01 4.20 4.91 4.13 5.26 3.50
3.95 3.30 3.65 4.19 5.29 3.39 2.35 3.80
Calcd. we. incr., % 18.6 12.6 15.7 16.5
Beforeb After iodina- iodination tion
... 4.70
5.09 2.31 2.83 3.34
4.87 5.17
__
Replaced by I
I, %
41.9 35.3
4.Olc 9.44 8.02 7.22
... 50.8
a All samples passed match test. I, Calculated by adding sulfur content after treatment to that which is equivalent to iodine in last column. Reaction in acetonylacetone solution of sodium iodide. ~
~
VOL. 50, NO. 1
~~
JANUARY 1958
93
~~
Table VI. Wt. Incr., %
7 11
Match Test Results on Modified Cotton Flame Char Derivative Held, Sec. Length, In. Cotton Oxford Bromo 2 2.2 Bromo 4 5.3 Iodo 2 0.5 Iodo
4
Iodo Iodo
6 6 6 6
Bromo Iodo
12 15 31 24 22
Bromo Bromo
6 6
1.8 2.5 2.0 1.8 1.8 3.3 n
Afterglow No No
Yes Yes Yes Yes No No No
No
Sateenh 19
4
7 6
18
6
10
14
6
Burned entire length.
+ +
A complete series of these derivatives, called mesyl 6-halocelluloses, was prepared from one mesyl cellulose sample. The per cent of halogens was normalized to per cent iodine, On the basis of numbers of atoms, substitution of chlorine was comparable to that of bromine and for fluorine, substitution was unusually heavy. Chlorine and fluorine seem to have little value as flame retardants; bromine is quite satisfactory but iodine is the most
Flame-Retardant Effect of Chemically Bound Halogens in Cotton Fabric As ,% Halogen % Iodine Rating" Br Ib
c1
3.95 4.01 1.45 2.11
6.2
4.01 5.2 13.9
Good
Excellent Fail Bail
F Match test (11). Reaction in acetoiiylacetone solution of sodium iodide.
94
No No No No No
Yes
A11 samples were bromo derivatives.
used in additive finishes for flameproofing research. Therefore, a method for introducing bromine into the cellulose molecule via a heterogeneous reaction was sought. A suitable method was discovered for preparing partially substituted iodo, bromo, chloro, and fluoro derivatives of mesyl cellulose. I n this method the difficulty caused by the relative insolubility of halogen salts (except iodide) in most organic solvents was overcome by the use of aqueous solutions of alkali halides. The pH of the reaction mixture had to be carefully controlled to avoid acid degradation of the fabric, The reaction is RO,11-OS02CH3 NaX aq. pH-7 -+Reell-X CH3S03Na BaC03 X = I, Br, C1, or F
+
1.5 2.8 1.0 1.4 2.0 2.8
INDUSTRIAL AND ENGINEERING CHEMISTRY
effective. Quantitative data are given for sulfur and halogen content of bromo and iodo derivatives in Table V. Replacement of sulfonyloxy groups by iodine has been reported by other investigators as almost quantitative (9). The data in Table V, however, indicate that mesylation is not highly selective for the 6 OH group because appreciable amounts of sulfur remain after iodine replacement. However, mesylation in the early stages is preferential for the 6 OH group. The results obtained on the first sample shown in Table V were consistent with this general pattern, but sulfur replacement data were not included because the reaction was carried out in an organic solvent under different conditions. The iodo derivative is more flame resistant than the bromo derivative, and Table V suggests that a more complete reaction occurs during iodine replacement. If per cent of bromine is normalized to per cent iodine, in three out of four experiments carried out under identical conditions, almost tivice as many iodine atoms are present in the iodinated samples than are bromine atoms in the brominated samples. The 6-iodo derivative is superior in flame resistance-it shows an average char length of 1.6 inches as compared with 3.3 inches for the 6-bromo derivative (Table VI). However, this superiority is a matter of degree, because the bromo derivative gives quite satisfactory results. For lightweight fabrics, it is unnecessary to increase fabric weight by a large percentage to obtain satisfactory flame resistance. A net weight increase of 10% seems sufficient, whereas most additive flame-retardant finishes require an add-on of about 20% for fabrics of 6 ounces per square yard, and even greater for very lightweight materials.
Glow resistance of heavily mesylated samples is generally good after halogen substitution, whereas that of lightly mesylated samples is poor. Modification by Phosphorylation. T o correct poor glow resistance, introduction of phosphorus, a well known glowretardant, was investigated. I t was also anticipated that if some 6 OH groups could be modified with an organophosphorus compound to form phosphorus-containing groups partially replaceable by halogen, then mesylation might be unnecessary. Such a derivative would contain halogen for flame extinction and phosphorus for glow resistance. For some mesyl derivatives, gloiv resistance was transitory--i.e., it was destroyed by continued application of flame to the char. Apparently the mesyl group with its sulfur atom provides temporary glow resistance and thus, for lightly mesylated samples, where a large proportion of these groups are located at the 6 carbon, halogen substitution removes many of the mesyl groups, resulting in ineffective glow resistance. Another explanation for this phenomenon is that sulfur volatilizes at continued high temperature, thus denuding the char of its protection against afterglow. It was thought that phosphorus would remain fixed in the char structure and thereby imparr permanent glow resistance. Methods extant for phosphorylation of cellulose have serious disadvantages such as fabric degradation and fabric sensitivity to alkali. A method which largely overcame these disadvantages was devised, and diethyl chlorophosphate was selected for study. The reaction is believed to follow the same mechanism proposed for mesylation, with diethyl chlorophosphate forming a pyridiniuni complex as the first step. The second step involves substitution of dieth)-1phosphonyl groups for labile hydrogen in the primary or secondary alcohol group to yield phosphocellulose. The first applications involved pretreating cotton oxford by wetting out and/or mercerizing, removal of excess water, and pyridine replacement of residual water followed by suspension of the samples in pyridine. Diethyl chlorophosphate was then added in a reagent to cellulose, mole ratio of 3 to 1 (Table VII). The reaction proceeds at an appreciably slower rate than mesylation and only a small percentage of phosphorus is required for glow resistance. All samples showed complete glow resistance that was indestructible under any conditions of test. I n the more heavily phosphorylated samples, no shrinking or curling resulted from burning and heavy char characterized by an intact fabric structure was produced. All samples exhibited moderate flame re-
,
CELLULOSIC FIBERS Table
VH.
Phosphorylation of Mesyl Cellulose and Cotton
(Room temp.) Reaction Time, Min. Wt. Incr., % ’ Mesyl Cellulose
Fabric Cotton oxford
Cotton 4.6 sq. yd.
30 5 5 4 5
oz./
4
4
Viscose rayon
6
5 5
8.0 3.9 3.2
1 .o
2.6 1.6 0.9 3.2 2.1 1.5
Cotton Reaction Time, Hr. Cotton oxford
52.75 36.5 14.0 3.5
19.3 6.5 2.5 2.0
sistance but, like mesylated cotton, failed the match test. Two samples were selected for halogen replacement. Although significant weight losses occurred (9.2 and 12.5Yo for bromination; 3.3 and 4.7% for iodination), there was no replacement of halogen; however, all samples retained afterglow resistance but failed the match test. This failure of halogen replacement precluded using this derivative as a precursor for a flame-resistant derivative in the place of mesyI cellulose. However, the glow resistance suggested that adding a few per cent of the diethyl phosphonyl group in a sample wherein mesyl groups and halogens had also been introduced would produce a combination derivative having good flame and glow resistance. Phosplibrylation was carried out before mesylation and halogen replacement Strip flame test Untreated controls were destroyed
but this had two serious disadvantages: 3 to 4 hours were required for the reaction, and fabric tenderization almost always resulted, However, if phosphorylation was performed on the mesylated fabric prior to halogen replacement, the process was improved, and the samples showed no afterglow (Table VII). An adequate level of phosphorylation can be: obtained using treatment times of 5 minutes or less. Also, phosphorylated samples showed no fabric deterioration. The mesyl cotton cellulose samples may be either dried prior to phosphorylation or treated directly after mesylation which requires no intervening washing step, although a pyridine rinse may be employed. A diethyl chlorophosphate-cellulose mole ratio of 3 to 1 was used. In Table VI11 phosphorus content of certain mesylated samples is shown. Less than 0.5y0 phosphorus is required for permanent glow resistance. The phosphorylated cellulose samples were extremely stable over a pH range of 6 to 11, and showed no afterglow. Flame and Glow Resistance. A series of combination derivatives called mesyl phospho-6-halocelluloses, prepared by phosphorylation, mesylation, and halogen replacement were tested (Table
Table
V111.
Phosphorus in Modified Cellulose
(Phosphorylation at room temp.) Fabric Oxford Sateen Sheeting Viscose rayon
Time, Min. LI
6 6 4 5 6 5
Not mesylated;
P, % 0.60 0.56 0.10 0.21 0.37 0.46 0.51
Calcd. Wt.
Incr., % ’ 2.7 2.5 0.43
0.91 1.6 2.0 2.2
reaction time, 36.5
hours.
IX). All samples were given two laundering cycles using both soap and detergent before flame testing. An over-all weight increase of 10% is sufficient modification to impart good flame and glow resistance to both cotton and rayon, Over the weight range of 3.6 to 9 ounces per square yard, chemical modification as described here can produce fabrics capable of passing the most rigid requirements for flame and glow resistance. In Table IX, none of the samples showed afterglow. Thus far, these modified fabrics have
Vertical Flame Tests Cotton Sateen
VOL. 50, NO. 1
JANUARY 1958
95
Table IX.
Fabric Sateen Cotton oxford
Flame Resistance of Modified Cellulosic Fabrics“
Wt., Oz./Sq. Yd! 9.0
8.1 10.9 16.5 10.9 15.6 7.3 8.2 13.0 15.3 18.0
6.0
Cotton sheeting
4.6
Viscose rayon
3.6
Wt. Incr., % Halogen 8.00 I, Br 9.OC I 12.5 I, Br
Br
I I, Br I I
Br Br Br Br I
a No samples showed afterglow. Untreated fabric. burned entire length. e Two samples burned entire length.
Flame Test, Char Length, In. Vertical Match, rating 3.5 Excellent 4.2 Excellent Excellent 3.6 Faird 5.5 5.2 3.9 6.2 5.8 5.3 6.0
...
5.2
...
Approximate.
Good
Excellent Fail
Excellent Goode
Good Good Excellent Good
One sample
method for introducing bromine as well as other halogens into carbohydrate molecules has been devised. Substantially any organic sulfonyl chloride may be used to prepare similar derivatives and the reactions discussed are applicable to materials other than cellulose-availability of la bile hydrogen and compatibility with tertiary nitrogenous organic bases are the limiting factors. I n preliminary experiments wood pulps and paper have been modified.
Acknowledgment
The authors gratefully acknowledge the laboratory assistance of Polly K. Way. They are indebted to John H. Menkart for the data on abrasion resistance, and to Dr. Ludwig Rebenfeld for not been produced in sufficient quantity termediate mechanism. By depolymersome of the cotton samples. Permission for tests such as tear strength, breaking ization and intramolecular rearrangement, 1,6-anhydro-/3-~-glucopyranose-of the sponsor to publish these data is strength, and flex abrasion. However, as appreciated. previously mentioned, no appreciable (levoglucosan) is formed as a first step and acts as a common intermediate, losses in tensile strength resulted from Literature Cited mesylation. Tests of flex abrasion reAlso, cellulose flammability arises from decomposition of levoglucosan into volsistance for combination modifications (1) Bernoulli, A. L., Stauffer, H., Helu. atile and flammable products. were run wet on I-inch raveled strips Chim. Acta 23, 627 (1940). which had been soaked overnight in Chemical modification of cellulose (2) Compton, J., J . A m . Chem. SOC.60. 395 (1338): . to reduce the levoglucosan-forming pobuffer solution (borate, p H 9.2). The (3) Cramer, F. B., Purves, C. B., Zbid., 61, results are: tential of the polymer and to introduce 3458 11939). elements that act chemically on the (4) Helferici, B.; Gniichtel, A., Be?. flaming gases is suggested as a method deut. chem. Ges. 71, 712 (1938). (5) Zbid., 74B, 1035 (1941). to impart flame resistance. This To (6) Hess, K., Ljubitsch, N., Ann. 507, 62 has been achieved by esterifying celFabric State Failures (1933). lulose hydroxyl groups with methane(7) Ivanov,’V. I., Golova, 0. P., PakCotton oxford Gray 620 sulfonyl chloride and partially replacing homov, A. M., Zzuest. Akad. ,%‘auk. mesyl phospho 780 S.S.S.R., Otdel. Khim. Nauk 1956, Sateen Gray 590 mesyloxy groups by bromine and/or No. 10, p. 1266. mesyl phosphoiodine. Glow resistance has been ob(8) Leiser, T., Schweizer, R., Ann. 519, 6-bromo 620 tained by introducing phosphorus-con271 (1935). a Mean cycles. taining groups in another esterification (9) Oldham, J. W. H., Rutherford, J. K., J . A m . Chem. SOC. 54, 36G (1932). reaction. The resultant derivatives, (10) Parks, W. G., Esteve, R. XI., Jr,, using cellulosic fabrics as starting Gollis, M. H., Guercia, R., PeThese results are not of precise quantitasamples, constitute new textile matrarca, A., “Mechanism of Pyrotive significance because structure of terials. lytic Decomposition of Cellulose,” 127th Meeting, ACS, Cincinnati, the treated fabrics is substantially difIodine is an effective flame retardant. Ohio, April 1953. ferent from the controls. However, I n chemical combination with cellulose, (11) Reid, J. D., Frick, J. G., Jr., Arcethey suggest that flex abrasion resistance halogens in order of their efficacy as neaux? R. L., Textile Research J . is unimpaired and augur well for all flame retardants are iodine, bromine 26, 137 (1956). (12) Schwenker, R. F., Jr., Pacsu, E., ENG.DATA IND.ENG.CHEM.,CHEM. SER.2, 83 (1957). (13) Shriner, R. L., Fuson, R. C., “SysBreaking Strength of Cottons Resistant to Flame and Glow tematic Identification of Organic Oxford Sateen Compounds,” 3rd ed., pp. 52-7, Wiley, New York, 1948. Test Control Modified Control Modified (14) Simmons, R. F., Wolfhard, H. G., Wt. incr., % 16.5 12.5 Trans. Faraday SOC. 51, 1211 (1955). Breaking strength, lb. 90.5 80.2 150.0 139.6 (15) Sugihara, J. M., “Advances in b b Char I., ha 3.9 3.6 Carbohydrate Chemistry,” vol. 8, Match teat Fail Pass Fail Pass pp. 1-44, Academic Press, New York, 1953. Vertical flame test. Burned entire length. (16) Tipson, R. S., Zbid., pp 108-215. (17) Wolfrom, M. L., Sowden, J. C., Metcalf, E. .4.,J . Am. Chem. SOC.63, 1690 (1941). important mechanical properties. Also, chlorine, and fluorine. I t is concluded that flame resistance shown herein is cottons were tested for breaking strength. RECEIVF~D for review June 15, 1957 ACCEPTED, August 8, 1957 caused by diminution in quantity of Raveled strips 6 inches long and 1 inch wide were broken on an Instron tensile flammable products and by release of Division of Cellulose Chemistry, Sympobromine or iodine in elemental or free tester with results as shown above. sium on New Chemically Modified Celluradical form to act as a chemical inhibitor losic Fibers, 131st Meeting, ACS, Miami, Fla., April 1957. Sponsored by the Office to flaming. Summary and Conclusions of the Quartermaster General, Department Two new cellulose derivatives, mesyl of the Army, through the Quartermaster Thermal degradation of cellulose is 6-bromocellulose and mesyl 6-fluoroResearch and Development Command, believed to proceed via a common incellulose, have been prepared. A simple Natick, Mass.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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