of the ivood resulting from the volumetric shrinkage upon ammonia removal. Of course, a t a given temperature and relative humidity the treated wood attains a higher equilibrium moisture content, \vhich further increases the dielectric constant. But \Then comparison is made a t the same moisture content, the dielectric constant is proportional to bvood density just as has been found for various unmodified woods (4, 5). Direct current resistivity of treated Wood decreases substantially relative to untreated wood a t the same moisture content (Figure 12). Charge conduction through wood is by ions (2). Because of the volumetric shrinkage caused by ammonia treatment, a decrease in resistivity is to be expected on the basis of a higher ionic density, other things being equal. O n this basis the resistivity should decrease by only 20 %, but the observed decrease is by more than one order of magnitude. Treatment Lvith anhydrous liquid ammonia a t a pressure of 1 atm. can yield ammonium salts from free carboxylic acid groups ( 7 ) . Small concentrations of such salts are probably responsible for the decrease in resistivity observed. Other mechanisms ma) be acting as well-for example, ammonolysis of esters occurs to produce acid amides ( 5 ) . However, ammonia in liquid phase a t room temperature existed in the
wood specimens a very short time under our treatment conditions and the mechanism probably contributes little to the conductivity. Ac knowledgrnent
The assistance of Conrad Schuerch, Mary P. Burdick, Miroslav Mahdalik, and Richard Elliott and financial support by the Sational Science Foundation are gratefully acknowledged. literature Cited (1) Bjorkvist, K. J., Jorgensen, L., .4cta Chern. Scand. 5 , 978 (1951 ). ( 2 ) Murphy, E. J., J . Phys. Chem. 33, 509-32 (1929). (3) Schuerch, C., Burdick, M. P., Mahdalik, M., IND.EXG.CHEM. PROD.RES.DEVELOP. 5,101 (1966). ( 4 ) Skaar. C., State University College of Forestry, Syracuse, N. Y., Tech. Publ. 69 (1948). ( 5 ) TVong. P. Y.:Balker, H. I., Purvis, C. B., Can. J . Chem. 42, 2434-9 (1964). ( 6 ) Yavorsky, J. M., State University College of Forestry, Syracuse, K. Y.,Tech. Publ. 7 3 (1951). RECEIVED for review October 13, 1965 ACCEPTED January 24, 1966 Division of Cellulose, \Vood and Fiber Chemistry, 150th Meeting, ACS, Atlantic City, N. J., September 1965.
VALERIC ACID ESTERS OF CELLULOSE J. W. M E N C H , BRAZELTON FULKERSON, AND G. D. H l A T T Cellulose Technology Division, Eastman Kodak Co., Rochester, .V. Y.
Cellulose valerate as well as the mixed cellulose acetate, propionate, and butyrate valerate esters have been prepared economically b y the conventional acid-anhydride-sulfuric acid catalyst procedure. Cellulose propionate valerate containing about 8y0 propionyl exhibits properties similar to those of cellulose trivalerate. This ester, prepared from water-activated, propionic acid-dehydrated cellulose, was selected as representative o f this class of esters for a study o f properties. The properties of cellulose propionate valerate are more like those of the higher fatty acid esters o f cellulose than those of the lower (C, to C,) esters. It shows a low melting point, high moisture resistance, good heat stability, and compatibility with a wide variety of resins and plasticizers, forms flexible compositions with several waxes, and has good adhesion to glass, metal, and paper. The ester i s soluble in a wider variety o f organic solvents than any other aliphatic ester of cellulose.
c
esters of aliphatic acids above butyric have never been manufactured in quantity, either because of the cost of the acids or because they must be prepared by uneconomical methods. However, their low melting point and high water resistance should prove desirable for some uses (8). Cellulose caprate is prepared and sold as a cement for lenses and optical systems (4, 73, 74) and it, as well as some of the other higher fatty acid esters, has been proposed for use in adhesives and for heat sealing (7). The chloroacetic anhydride method (7) used for the preparation of cellulose caprate is not practical for large scale production and has limited the potential uses of this and the other higher cellulose esters to those in which cost is not a n important factor. Thus, a different method of preparing these esters or other similar esters that could be prepared more economically is needed. Valeric acid has become available a t reasonable cost and a practical method of making its cellulose esters has been developed (5). The esters containing high proportions of valeryl have properties more like those of the higher fatty acid esters than those of the lower (C, to C , ) acids. This paper describes ELLULOSE
110
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
some of the properties of these esters, with special emphasis on cellulose propionate valerate containing about 8% of propionyl. Preparation
Contrary to statements in the literature (771, valeric acid esters of cellulose are readily prepared by conventional esterification procedures using water-activated cellulose. valeric anhydride, and sulfuric acid catalyst (6). Cellulose Valerate. One part of cotton linters was activated by soaking in distilled Lvater for 16 hours and, after centrifuging, the water was displaced with methylene chloride or valeric acid. The dehydrated cellulose was then placed in a Werner-Pfleiderer type of mixer with 4.5 parts of valeric anhydride and the esterification conducted a t 80' to 100' F. using from 0.02 to 0.08 part of sulfuric acid catalyst. The viscosity of the product is regulated by the reaction time, temperature, and amount of catalyst used. \\'hen a clear, grainfree solution was obtained, a 5070 excess of magnesium carbonate was added over that required to neutralize the sulfuric acid used and the reaction mass was raised to 245' to 250' F. for 3 hours. This replaced combined sulfate with valeryl and
stabilized the product ( 2 ) . The resulting reaction solution was then cooled, diluted with acetic acid, and filtered to remove magnesium sulfate and any unreacted fiber. The ester was isolated from the filtered solution, after dilution with acetic acid, by precipitation into 40 to 50% aqueous acetic acid. The product was washed with changes of progressively weaker aqueous acetic acid and finally with water until the ester was acid-free. T h e material was centrifuged after the final wash and dried a t 120' F.
conventional procedure, consisting of adding sufficient water to the esterification solution, without neutralizing the sulfuric acid catalyst, to destroy the excess anhydride and to provide 5 to 10% water in the bath. Portions of the mixture were taken at desired intervals and the ester was isolated as previously described.
The cellulose trivalerate and some commercial cellulose esters were regenerated to cellulose with methanolic sodium methoxide (70) and their intrinsic viscosities determined in 0.3M iron-sodium tartrate (FeTNa) solution. Approximate degrees of polymerization of the materials are shown in Table
Melt Behavior. MELTINGPOINT. Melting points of the valeric acid derivatives (Table 11) were determined by heating the esters in a 4-mm. glass tube in a copper block with temperature rise controlled at 5' C. per minute. The melting points of the acetate valerates increase with increasing amounts of combined acetyl, whereas the propionate valerates (at the same general viscosity level) and butyrate valerates show no real variation in melting points over the ranges of composition investigated, nor do their melting points differ appreciably from that of cellulose trivalerate. Variations in the method of determining the melting point can give different values. Thus, slower heating rates and especially the application of pressure to the sample can produce clear melts a t lower temperatures. A wide range in melting point may also be obtained by varying the viscosity of the esters as shown for a series of fully esterified cellulose propionate valerates of 8% propionyl content (Figure 1). Hydrolysis of the esters also affects the melting point (Figme 2 ) . Hydrolysis of the simple valerate ester and of the propionate valerate (8% propionyl) gives minimums in the melting point curves as the percentage of hydroxyl increases; this is similar to the results obtained by hydrolysis of propionate and butyrate esters of cellulose ( 5 ) . HEAT-SEALISG CHARACTERISTICS. Heat-sealing tests were run on two samples of cellulose propionate valerate having inherent viscosities in acetone of 0.25 and 1.19 (Table 11). The tests were conducted by placing a small amount of the ester between sheets of 18-mil board stock and making the seals b a t a constant pressure with a 3-kg. electric iron. The temperature of the iron was measured with a pyrometer and the contact time was varied. T h e data obtained (Figure 3) are compared with those for a sample of cellulose caprate and two Vinylite resins. The higher viscosity propionate valerate seals satisfactorily over a temperature range of 300' to 600' F., whereas the low viscosity ester has a narrower operating range-i.e., about 320' to 480' F. ; above 480' F. the melt is too fluid for good adhesion. Cellulose caprate, being a lower melting derivative than the two propionate valerates tested, can be sealed a t a lower temperature. Useful operating temperatures for all of the cellulose derivatives cover a much wider range than those of thevinylites. There is, of course, a n optimum contact time for good sealing with any of the materials in a given temperature range that would also depend on the thickness of the paper or board being sealed.
I. Mixed Esters. Cellulose acetate, propionate, and butyrate valerates were prepared by dehydration of the water-activated linters with the corresponding lower fatty acid, followed by esterification with valeric anhydride. The amount of lower acyl radical introduced was varied by changing the ratio of lower acid to valeric anhydride in the esterification bath. Analytical data on typical esters (essentially triesters of cellulose) prepared by the foregoing two methods are shown in Table 11. Linters dehydrated with propionic acid retain about 0.8 part of the acid after centrifuging and after reaction with 4.5 parts of valeric anhydride produce cellulose propionate valerates containing about 8% of propionyl and 51% ofvaleryl. Esters of this composition were considered representative of high valeryl content products and, unless otherwise specified, are the materials whose properties are described. Esters Containing Hydroxyl. Cellulose propionate valerate and cellulose trivalerate were hydrolyzed by the
Table 1.
Degree of Polymerization of Cellulose Valerate and Other Cellulose Esters
Cellulose Ester
Inherent ViscoJ ity" in Acetone Pyridine
Intrinsic Viscosity of Regenerated cellulose in F e T N a
~ p p ~ ~ ~ .
D.P.
Trivalerate 0.80 ... 1.17 170 Capratec ... 0.20 0.54 78 Acetate d 0.94 0.78 1.21 175 Acetate e 1.55 1.35 1.80 261 a Determined at concentration of 0.25 /lo0 ml. Using factor 145 X intrinsic viscosity ( F e T N a ) = LfP. Cellulose tridecanoate, Eastman Organic Chemical P-7737. Eastman cellulose acetate E 398-3. Eastman cellulose acetate E-394-30. @
Table 11.
Type of Ester Acetate-valerate
Propionate-valerate
Valeric Acid Esters of Cellulose Inherent MeltViscosity ing in Composition, wt. % Point, C. Acetone" Acetyl Valeryl
0.31 0.48 0.65 0.43 0.51 0.74 1.02 1.19
Butyrate-valerate
8.9 15.9 21.8 Propionyl 6.2 11.7 8.1 8.4 8.8 Butyryl 2.2 10.9 15.6
Mplt ~
Shear Temp., O C.
49.1 39.0 31.3
124 145 159
122 129 134
54.0 47 4
128
119
113
51.2 51.0 50.8
120 136 145 145
...
127 133 133 130
141 144 145
0.32 59.0 0.52 49.7 0.63 45.0 Trivalerate 0.80 ... 61.0 Determined at concentration of 0 . 2 5 g . / l O O ml.
,..
,.. , ,.
...
Properties
TACK A N D BLOCKING TEMPERATURES. Tack temperatures were determined on the same materials tested as heat sealants. T h e materials were applied on glassine paper by solvent coating and curing, then strips of the coated paper were pressed into contact with a chromium-plated metal bar, heated so that there was a temperature gradient from one end to the other. After a contact time of 1 minute the strips were pulled u p from the cool end of the bar, and the temperature of the bar a t the sticking point was determined with a pyrometer. Blocking temperature of the coated papers was determined by placing two strips together with the coated sides in contact and holding the samples in a n oven for 16 hours under a weight giving a contact pressure of 5 p.s.i. The first set of samples was run a t 150' F. and the oven was then adjusted up or VOL. 5
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down in 20' to 30' steps, depending on whether or not the samples blocked a t 150'. The data obtained are shown in Table 111. T h e higher viscosity propionate valerate shows desirably high tack and blocking temperatures which, of course, reflect its higher melting point, which in turn leads to higher sealing I
I
1
I
I
I
temperatures. All of the cellulose derivatives show higher blocking temperatures than the Vinylites. MELTVISCOSITY.Melt viscosities were determined on two samples of cellulose propionate valerate having inherent viscosities in acetone of 0.25 and 0.72, respectively. T h e melts were made in 38 X 150 mm. test tubes which were heated in a constant temperature bath, and a '/lt-inch steel ball was used for the determination. T h e viscosities were first measured a t 185' C. and then a t progressively lower temperatures down to 145' C. T h e data (Figure 4) are compared with those for a cellulose caprate, two low-viscosity polyethylenes [Epolene C and Epolene N ( 3 ) ] ,and a plasticized cellulose acetate butyrate [EAB-500-1 plus 25 parts of butyl sebacate-butyl stearate 60:40 ( g ) ] . The higher viscosity propionate valerate ester has melt viscosity characteristics similar to those of the plasticized cellulose acetate butyrate: whereas the lo\v viscosity propionate valerate has characteristics approaching those of the cellulose caprate and Epolene N. Epolene C falls about midway between the two cellulose propionate valerate esters. VISCOSITY A N D COLORSTABILITY.Portions of a cellulose propionate valerate were held melted a t 160' C. for various
Inherent viscosity in acetone I I CELLULOSE CAPRATE I.V. 2 0.25, M.P. = 90'C.
I
Figure 1. Relation of melting point of cellulose propionate valerate to inherent viscosity in acetone
5
I
I
2
131
(SECONDS)
CELLULOSE PROPIONATE VALERATE I V = 119, M P = 145OC. 20
1
170k
I 10 I
1
5
2
CELL. PR. VAL. I V : 0 25, M.P. = 120°C 20 I 10 I 5 13
(Vi ny I i t e ) 20 IO
m(Viny1ite) I 300
I 200
2010 2
1
I
I
400
500
600
Sealing temperature "E Figure 3. Heat-sealing ranges of cellulose propionate valerates and some other polymers Contact time indicated in seconds
h 1
2
3
100,oot
4
I
I
I
I
I
I
Percent Hydroxyl Figure 2. Relation of melting point of valeric acid esters to per cent hydroxyl
0
Cellulose valerate A Cellulose propionate propionyl)
2 10,001 .VI
valerate
(8%
P 0
._ e c
U
s
e ._ v)
Table 111. Material Tested
Tack and Blocking Temperatures Blocking Sealing Tack Melting Point, Temp., Temp., Qmp., F. F. F. F. a
Cellulose propionate 248 165 120 350 valerateb Cellulose propionate 293 265 174 370 valeratec 194 165 150 250 Cellulose caprate ... 165 100 250 Vinylite AYACd ... 180 100 235 Vinylite AYXAd Inherent oiscosity in a From Ftgure 3, contact time 70-75 seconds. acetone, 0.25. Inherent ciscosit?; in acetone, 7.79. Union Carbide.
112
I & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
=:
I;j
1,oo
IO-
----&-A 140
150
160
170
180
190
1
lengths of time and measurements were made of melt color and inherent viscosity of the products (Table IV). T h e material has good viscosity stability and a moderate color stability that can be improved by treating the ester with a small amount of p-tert-butylphenol. This test was devised in a n MELT SHEARTEMPERATURE. effort to correlate melting points of the esters with their flow characteristics and consisted of cementing two glass slides together and determining the temperature a t which they separated under tension.
A small amount of ester was placed on a 1 X 3 inch microscope slide, then melted by careful heating over a Bunsen flame. A second prewarmed slide was then placed over the first with an overlap of 1 inch. T h e cemented slides were suspended vertically in a circulating air oven and tension was applied to the bottom slide with a 100-gram weight. T h e oven temperature was raised at a rate of 1' to 2' C . per minute until the ester floived sufficiently for the slides to separate. Five tests \Yere made on each ester and the average temperature a t Fvhich the bonds failed is designated the melt shear temperature. The melt shear temperature (Table 11) is lower than the ester melting point for the acetate valerates and propionate valerates but higher than the melting points in the case of the butyrate valerates. This shows that the butyrate valerates are not so subject to flow below their melting points. FLUIDIZEDBED COATINGS.Finely ground cellulose propionate valerate was fluidized with air in a fritted glass funnel fitted with an extended top of transparent plastic film. Previously heated test tubes were dipped into the fluidized ester for 1 to 2 seconds, then removed, and the adhering ester was reheated to effect flow and complete coverage of the glass surface with a clear film. 'The low melting point and good heat stability of the ester allow this to be done without addition of plasticizer. Solubility. Cellulose trivalerate is the most widely soluble of the aliphatic esters of cellulose (8). Solubility characteristics of the valeric acid esters containing small amounts of acetyl, propionyl, or butyryl are virtually identical with those of the trivalerate. Typical viscosity-concentration curves for a cellulose propionate valerate having a n inherent viscosity in acetone of 1.02 are shown in Figure 5 along with the densities of the solutions. Compatibility. A cellulose propionate valerate having an inherent viscosity in acetone of 1.02 was tested for its compatibility with a variety of resins, plasticizers, and waxes. RESINCOMPATIBILITY. Compatibility with resins was tested by dissolving the ester a t a 20y0 concentration in a lacquer solvent mixture (17% xylene, 25% toluene, 33y0 butyl acetate, 10% butanol, and 15% 3A alcohol) and adding the resin after the ester had dissolved. The resins were added as 25y0 of the weight of the ester, and the compatibility was observed both in the solutions and in film tabs coated from the solutions. Some resins giving both clear solutions and clear film tabs are shown in Table V. PLASTICIZER COMPATIBILITY. T h e cellulose propionate Valerate was found to be compatible with dioctyl phthalate, di-
Table IV. Viscosity and Color Stability of Cellulose Propionate Valerate Time of Heating, Hours .~ 0 2 4 7 76 Color ( APHA) ... 200 400 600 2000 0.58 0.57 0.38 Inherent viscositya 0.63 0.61 a I n acetone.
butyl sebacate, and triphenyl phosphate when these were mixed with the molten ester a t concentrations up to 20% by weight. Since the valerate esters are the most widely soluble of all the cellulose esters of aliphatic acids, they would be expected to have equally wicl compatibility with plasticizers. Because of the low melting ioints of the esters, however, the addition of even small amounts of these plasticizers produced soft and tacky compositions. WAXCOMPATIBILITY. These tests were conducted by melting together 4 parts of the cellulose propionate valerate, 1 part of dibutyl sebacate, and 1 part of the wax, then pouring the melts onto glass plates and allowing them to cool. As shown in Table VI, clear compositions were obtained with Chlorowax 40 and Carbowax 1500. I n other instances the color and opacity were influenced by the modifying wax although flexible compositions were obtained.
100,000
I
I
I
1
10,000
cn a, .E 1,000 0
a .c
i
3
t W V
s
c
100
1
' :1
0
u
.-m
> 10 0.8
cn
Ester
I
~==,",.. concentrotion
I
I
I
I
IO
20
30
40
(Yo)
I
Ester concentration (%) Figure 5. Relation of viscosity to concentration of cellulose propionate valerate solutions Inherent viscosity, 1.02
Table V. Resins Compatible with Cellulose Propionate Valerate in Lacquer Solvent and in Films Trade Name of Resin Amberol 820" Arochlor 5460* Dewaxed DammarC Durez 219d Flexalyn C e Polypale ester 1* Polypale ester 101 Krumbhaar 17170 Linde X-12* Newpcrt V-40i Paraplex G-52a Uformite 240" Uformite 6 l Q a Rohm and Haas. Monsanto. Durez. e Shawinigan. f Hercules. h Linde. i Newport Industries.
VOL. 5
Type Maleic-rosin Chlorinated biphenyl Natural Terpene-phenolic Ethylene glycol-rosin G1ycol-rosin Glycerol-rosin Ketone-aldehyde Silicone Pinene Polyester Urea-formaldehyde Urea-formaldehyde Archer Daniels i'lidland Go. g Krumbhaar Chemicals, Inc.
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Table VI.
Compmlibility of Cellulose Propionate Valerate with Dibutyl Sebacata and Waxes WOX
Chlorowaa 4OS Castor wax Candelilla wax Japan wax Carnauba wax Ceresin Halowaxb Carbowax 1500( Stearic acid
Diamond Alkolt.
(4:l:l) Appcorance of Cooled Mdt Clear, tan, flexible Hazy, yellow, flexible Hazy, yellow, flexible Hazy, light, flexible Opaque, brown, flexible Opaque, light, flexible Opaque, light, flexible Clear, flexible Opaque, white, flexible Halowax Products.
Union Carbidc.
Table VII.
Sward Hardness of Cellulose Propionate Valerate Compositions
Amount, Additiue None (unmodified ester) Arochlar 5460 Arochlor 5460 Paraplex G-62 Paraplex G-62 Polypale ester 10 Uformite 240 Uformite 61 Chlorowax 40 Dioctyl phthalate Cellulose nitrate wood lacquers Half-second butyrate aluminum lacquer Air-dlying varnishes Cellulose acetate butyrate (EAB-381) White shellac Low viscosity polyethylene a
Plcte glass =
Table VIII.
left
X-ray diegram of ce
Coded from benzene-melhon 01
sn 25 25 25 25 25
36 23 16 8 14 29
23 22
io 6 40-50 42 16-20 50 34 6
Variation of Physical Properties of Cellulose Propionale Valerate Films with Hydrolysis r v l d " - * D-pionote Volerole B C
Physical Rofiwtiu Thickness of films. mils
7.
25 50 25
Sward Hardness-
loo.
%H Inhe
Figure
% ..
6.5
1.7 0.82
2.8 0.75
6.4
6.5
S\VARDHARDNESS. Sward hardness was determined on films of the cellulose propionate valerate both with and without added resins, plasticizers, or wax. As shown in Table V I I , all of the addends produce compositions of lower hardness than unmodified propionate valerate, which has a hardness about equal to that of white shellac (72). Physical Properties. Tensile strength, elongation, and folding endurance were determined on cellulose propionate valerates of increasing degrees of hydrolysis (increasing hydroxyl contents). The properties were determined on films coated onto glass plates from filtered benzene-methanol (90 to 10) solutions. The stripped films were cured 48 hours a t 130” F. to decrease residual solvents to a minimum, and the tests \vere conducted on strips cut both along and across the coating direction ; these measured 15 x 180 mm. with a thickness of 6.5 mils. For tensile and elongation measurements, a S h o p p e r tensile tester with a cross-head speed of 4 inches per minute was used, and the results have been calculated in terms of pounds per square inch of starting cross-sectional area. As shown in Table VI11 and Figure 6: tensile strength increases and folding endurance decreases with increasing hydroxyl content of the esters. The elongation of the films a t the breaking point shows little trend lvith hydrolysis. Physical properties of films. of course, are dependent on the coating conditions-i.e., solvents used and degree of curing. The properties reported thus must be considered to shoiv only trends. Films of these esters coated from acetone, for example, are extremely brittle and may shatter upon removal from the glass plates even when they contain 5 parts of dibutyl sebacate as plasticizer. In the case of sample A (Table VIII), the most
nearly fully esterified ester, greater crystallinity is observed when coated from acetone us. benzene-methanol, as shown by x-ray diagrams (Figure 7). This is not true for the two hydrolyzed esters (samples B and C), since x-ray diagrams of these films, coated from either solvent, showed them to be amorphous. literature Cited
( 1 ) Clarke, H. T., Malm, C. J., U. S. Patent 1,880,808 (Oct. 4,
1932). ( 2 ) Crane, C. L.. Zbid., 3,047,561 (July 31, 1962). ( 3 ) Eastman Chemical Products Bulletin, “Epolenes,” 1959. (4) Field, D. E., Fox. R. B., “Hydrolytic iModification of Cellulose Caprate,” Naval Research Laboratory Rept. 4948 (May 23, 1957). ( 5 ) Malm, C. J., Fordyce, C. R., Tanner, H. A., 2nd. Eng. Chem. 34. 430 11942). (6) Malm, C. J., Fulkerson, B., Mench, J. I V . , U. S. Patent 3,103,506 (Sept. 10, 1963). ( 7 ) Malm, C. J., Hiatt. G. D., Zbzd., 2,324,097 (July 13, 1943). ( 8 ) Malm, C. J., Mench, J. \Y., Kendall, D. L., Hiatt, G. D., Ind. Ene. Chem. 43. 684 f 19511. 9 ) Malm: C. J., Saio, M., Vivian, H. F., Zbid., 39, 168 (1947). 10) Malm, C. J., Tanghe, L. J.: Herzog, H. M., Stewart, M. H., Zbid..50, 1061 (1958). 11) Ott, E., “Cellulose and Cellulose Derivatives,” Vol. V, p. 730. Interscience, S e w York, 1954. 12) Payne, H. F., “Organic Coating Technology,” Val. 1, p. 643, Il’iley, New York, 1954. 13) Tanner, H. A , Rogovin. A , : Lockhart, L., “Cellulose Caprate Cement,” Naval Research Laboratory Rept. P-2691 (Dec. 3, 1945). 14) U. S. 1)epartment of Commerce, “Improved Cellulose Caprate Optical Cement,” Rept. P B 111273 (Sept. 8, 1953). RECEIVED for review November 18, 1965 ACCEPTED April 8, 1966 Division of Cellulose, Wood, and Fiber Chemistry, Winter Meeting, ACS, Phoenix Xriz., January 1966.
DIRECT PROCESS FOR PREPARATION OF SMALL PARTICLE CELLULOSE NITRATE A L A N M. B E L F O R T A N D R O B E R T B. W O R T 2 American Viscose Division, Avicel Department, FMC Corp., Marcus Hook, Pa.
Small particle cellulose nitrate was prepared by a direct process starting with microcrystalline cellulose. Nitrations were performed in a high solids reactor using low weight ratios of nitrating acid mixtures. Nitrating acid mixtures were added to the cellulose raw material. Some other conventional steps were eliminated: nitrating acid recovery, kiering viscosity control, and the solvent emulsion technique for preparing densified particles from fibrous cellulose nitrate. The small particle cellulose nitrate product had an average particle size of 2.4 microns, a high bulk density, and a homogeneous molecular weight distribution.
nitrate has been a versatile product in plastic, and propellant applications for more than a century. “Soluble” grade cellulose nitrate was used for photographic film, artificial leather, and quick-drying lacquers for automobiles and is still a major ingredient in formulations for furniture lacquers, multicolor lacquers, and cloth coatings. “Smokeless” grade cellulose nitrate was first used in large volume as a ballistic propellant during TYorld War I. Recently, major solid propellants containing cellulose nitrate have been perfected for long-distance ballistic missiles and for space rockets. Two small particle forms of cellulose nitrate were recently introduced : Plastisol grade nitrocellulose (E.I. d u Pont de Nemours BL Co.) is recommended for commercial and miliELLULOSE
C lacquer,
tary uses; nitrocellulose in organosol form (Hercules Powder Co.) is used in a iviping filler for furniture. Densified forms of cellulose nitrate are made from fibrous cellulose nitrate by solvent emulsion techniques (3, 9, 70). Fibrous cellulose nitrate is dissolved or swollen in a solventnonsolvent mixture, the mixture is subjected to high shear to form a globular dispersion, and small particles of cellulose nitrate are precipitated by evaporation of the solvent. Fibrous cellulose nitrate raw material for densification is manufactured by a process which has changed little since 1845. Improved continuous nitration (5) was recently introduced but processing disadvantages still persist. Fifty parts of nitrating acid are used for each part of cellulose to obtain intimate contact (5) of the reactants. T h e nitrating acid mixture VOL. 5
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