US2202804A

US2202804A - Cellulose acetate composition

Info

Publication number: US2202804A
Application number: US159110A
Authority: US
Inventors: Herbert L Wampner; Bogin Charles
Original assignee: Commercial Solvents Corp
Current assignee: Commercial Solvents Corp
Priority date: 1937-08-14
Filing date: 1937-08-14
Publication date: 1940-05-28
Anticipated expiration: 1957-05-28

Description

Patented May 28, 1940 I UNITED STATES CELLULOSE ACETATE COMPOSITION Herbert L. Wampner and Charles Bogin, Terre Haute, Ind.,' assignors to Commercial Solvents Corporation, Terre Haute, Ind., a corporation of Maryland No Drawing.

Application August 14, 1933,

Serial No. 159,110

3 Claims.

Our invention relates to cellulose acetate compositions, and particularly to such compositions comprising cellulose acetate, nitro saturated nonbenzenoid hydrocarbons, and aliphatic alcohols.

While a great many satisfactory and readily available solvents have been suggested for nitrocellulose, relatively few solvents are available for cellulose acetate, and most of these are unsuited for general use on account of such factors as low T tolerance for diluents, solubility in water with resulting blushing tendencies, and especially unsatisfactory rates of evaporation.

An object of our invention is to provide solvent components for cellulose acetate compositions i which have a wide range of evaporation rates and which have general application for at least partially dissolving cellulose acetate. A further object of our'irivention is to provide cellulose acetate solutions which are particularly suitable for coating purposes, are free from blushing difficulties, and which may be varied in composition to secure diiferent rates of evaporation, etc. Other objects and advantages of our invention will be apparent from the following description.

The nitro non-benzenoid hydrocarbons containing 2 or more carbon atoms are not per se solvents for cellulose acetate. However, we have now found that when mixed with suitable proportions of monohydric aliphatic alcohols these nitro saturated non-benzenoid hydrocarbons are capable of at least partially dissolving the various commercial grades of cellulose acetate, and that combinations of these nitroparafllns, especially those of 2 to 4 carbon atoms, with lower allphatic alcohols are excellent solvents for the low acetyl grades of cellulose acetate commonly employed in coatingcompositions. Y

The nitro saturated non-benzenoid hydrocarbons which are suitable for use in accordance with our invention constitute the nitroparaflins containing 2 or more carbon atoms and the cycloalkyl and aryl substituted nitroparafllns. Among these-materials we prefer to employ the lower nitroparafllns such as nitroethane, 1'-nitropropane, 2-nitropropane, l-nitrobutane, l-nitroisobutane, and mixtures of such materials obtained by the nitration of saturated hydrocarbons.

Any monohydric aliphatic alcohol may be employed in our solvent mixtures but we prefer to utilize the lower members of this series, e. g., al-

cohols containing from one to six carbon atoms.

As will be pointed out below, we prefer 'to' employ only the alcohols of one to four carbon atoms in order, to secure clear solutions with certain types of cellulose acetate. The particular alcohol to be employed in any case will depend upon the -'other components of the composition and the results desired. Thus, if it is desired to deposit a clear film of cellulose acetate it will usually be necessary to include in the composition an alco- 5 ho] having an evaporation rate comparable tothe nitrohydrocarbon employed in order that the cellulose acetate may stay in solution throughout the evaporation of the solvents. If constant evaporating mixtures of any of the solvent components are formed, care should be taken to provide a proper ratio of nitrohydrocarbons to alcohols at all stages of the evaporation. Mixtures of alcohols may be found desirable from this and other standpoints, and one skilled in the art may la readily determine by preliminary experiments the best alcohol or mixtures of alcohols for any given purpose.

Our invention is applicable to any of the commercial grades of cellulose acetate ranging from the low acetyl, low viscosity, grades to the high acetyl grades known as cellulose triacetate. These different grades of cellulose acetate vary widely in solubility, the low acetyl grades, i. e., having acetyl numbers ranging from 36-38, being the most soluble, and the other grades decreasing in solubility with increase in the acetyl number. We have found that the solubility of the various grades of cellulose acetate also decreases, in general, with increase in the molecular weight of the nitrohydrocarbon and increase in molecular weight of the aliphatic alcohol. Thus, the solubility varies over a wide range from complete solubility of the low acetyl grades of cellulose acetate in mixtures of lower nitroparamns and lower aliphatic alcohols, to only partial solubility of the high acetyl grades of cellulose acetate in mixtures of the higher nitroparafllns and higher aliphatic alcohols.

Although clear solutions may be obtained with high acetyl grades of cellulose acetate in mixtures of the low molecular weight'nitrohydrocarbons of this group, and low molecular weight aliphatic alcohols, and clear solutions of the very low acetyl grades of cellulose acetate may be obtained in mixtures of the higher molecular weight nitrohydrocarbons and aliphatic alcohols, we have found that there is a definite group of compounds within which complete solubility occurs with proper proportions of all combinations of 5 0 cellulose acetate, nitrohydrocarbons, and aliphatic 'alcohols.f This group includes the grades of cellulose acetate having acetyl numbers "below 40, aliphatic alcohols containing from one to four carbon atoms, and nitroparaflins of the group consisting of nitroethane, l-nitropropane, 2-nitropropane, l-nitrobutane, and l-nitroisobutane.

Although complete solubility, with resulting clear solutions, is secured uniformly only within the group defined above, it is to be understood that our invention is not limited to this particular range of materials, but is applicable generally to the use of mixtures of nitro saturated nonbenzenoid hydrocarbons of 2 or more carbon atoms and monohydric aliphatic alcohols for at least partially dissolving cellulose acetate. In the cases in which the material is not completely dissolved, the solvent mixture serves as an excellent wetting and swelling agent, thus facilitating complete solution of the cellulose acetate in subsequently added solvents. In such cases our solvent mixtures are particularly desirable, since in conjunction with other cellulose acetate solvents they enable a considerable proportion of the relatively cheap aliphatic alcohols to be substituted for the more expensive active solvents. In some cases of incomplete solution, completely or partially gelled liquids are obtained which may be used in any manner in which such compositions are employed in the art. It is to be understood, therefore, that our invention includes all such compositions as well as clear solutions of cellulose acetate in the solvent mixtures.

In carrying out our invention the cellulose acetate is contacted with the mixture of nitro saturated non-benzenoid hydrocarbon and monohydric aliphatic alcohol to secure at least partial solution of the cellulose acetate. In view of the physical form of the cellulose acetate, it is desirable to agitate thoroughly-to effect as complete solution as possible. In certain cases, particularly compositions including solvent constituents of relatively high molecular weight, it is desirable to apply heat to aid in securing maximum solution. The application of heat will increase solubility in all cases, but after cooling to atmospheric temperature, some of the dissolved cellulose acetate may be thrown out of solution or the solution may subsequently gell unless a solvent mixture properly formulated to secure complete solution is employed.

The proportion of aliphatic alcohol to be employed in the solvent mixture will depend upon the nitrohydrocarbon and the alcohol utilized, upon the desired viscosity and flow characteristics, and upon the desired degree of tolerance for hydrocarbon diluents. In each case a definite minimum amount of alcohol is required to activate the nitrohydrocarbon, and this minimum amount increases with increasing molecular weight of the nitrohydrocarbon and of the alcohol. Thus, 25% of ethyl alcohol, based on the volume of the total mixture, will activate nitroethane sufficiently to dissolve low acetyl grades of cellulose acetate; whereas approximately of secondary butyl alcohol is required to activate l-nitroisobutane sufliciently to dissolve cellulose acetate of medium acetyl grade. For each combination of nitrohydrocarbon and alcohol there is also an upper limit of alcohol content for maximum solubility which decreases with increase in molecular weight. Thus, in the case of nitroethane and ethyl alcohol the upper limit of the alcohol content is approximately 75% by volume of the total mixture, whereas in the case of l-nitropropane and normal-butyl alcohol the upper limit of the alcohol content is approximately 60% of the total mixture. There is thus a range of proportions for maximum solubility which decreases in scope with increase in the molecular weight of the compounds.

As has previously been pointed out, other cellulose acetate solvents may be utilized in conjunction with solvent mixtures, and a small proportion of an auxiliary slow evaporating solvent may be found desirable from the standpoint of ease of formulation to insure complete solubility throughout the evaporation of the solvent mixture. Hydrocarbon diluents which are commonly employed in the art, such as benzol, toluol or petroleum hydrocarbons, may also be incorporated in the solvent mixture, and there will be a tolerance range for each particular combination employed, the tolerance tending to decrease with increase in molecular weight of the alcohol and nitrohydrocarbon. The trend of the range of composition of the solvent mixture may be seen from the above discussion and from the following specific examples, and one skilled in the art may readily determine by preliminary experiments a suitable composition for any particular purpose.

The following examples illustrate solutions of cellulose acetate in our improved solvent mixtures:

Example I A clear solution of cellulose acetate (acetyl number 38.0-40.0; 20% A. S. T. M. viscosity 2.0-5.0) was prepared by dissolving 10 parts by weight of this material in 100 parts by weight of the following solvent mixture:

Per cent by volume Nitroethane Ethyl alcohol Example II A clear solution of cellulose acetate (acetyl number 38.7-39.4; 20% A. S. T. M. viscosity 70.0-140.0) was prepared by dissolving 4 parts by weight of this material in 100 parts by weight of the following solvent mixture:

Per cent Nitrated propane Ethyl alcohol 35 n-Butyl alcohol 10 N itromethane Nitroethane 26 l-nitropropane 32 2-nitropropane 33 Example III A clear solution of cellulose acetate (acetyl number 40.1-40.5; 20% A. S. T. M. viscosity 18.0-23.0) was prepared by dissolving 6 parts by weight of this material in 100 parts by weight of the following solvent mixture:

Per cent by volume l-nitroisobutane Sec. butyl alcohol 35 Example IV A clear solution of cellulose acetate (acetyl number 37.0-38.5; 20% A. S. T. M. viscosity 1.8-4.5) suitable for use as a coating composition was prepared by dissolving 10 parts by weight of the cellulose acetate in 100 parts by weight of the following solvent mixture:

Per cent by volume Nitroethane 40 Ethyl alcohol 25 Toluol 35 Example V A clear solution of cellulose acetate (acetyl number 37.0-38.5; 20% A. S. T. M. viscosity 1.8-4.5) suitable for use as a coating composition was prepared by dissolving 10 parts by weight of the cellulose acetate in 100 parts by weight of the following solvent mixture:

Per cent by volume l-nitropropane 35 Ethyl alcohol 25 n-Butyl alcohol 10 Toluol 30 Example VI A clear solution of cellulose acetate (acetyl number 38.7-39.4; 20% A. S. T. M. viscosity 2.5-5.0) suitable for useas a coating composition was prepared by dissolving 10 parts by weight of the cellulose acetate in 100 parts by weight of the following solvent mixture:

Per cent by volume l-nitrobutane 50 n-Butyl alcohol 20 Toluol 20 Fusel oil amyl alcohols 10 positions for coating materials, for the deposition 7 of films, or for other known uses in the art. Likewise, numerous equivalents may be employed for the materials specifically mentioned in the examples, and, as has been previously pointed out, our invention is not limited to the production of clear solutions but is applicable generally in at least partially dissolving cellulose acetate. It is to be understood, therefore, that the use of any equivalents or modifications of procedure which would naturally occur to one skilled in the art is included within the scope of our invention.

Our invention now having been described, what we claim is:

1. A method of dissolving cellulose acetate of a grade having an acetyl number below 40 to produce a clear solution which comprises contacting the cellulose acetate with a mixture of a nitroparaffin chosen from the group consisting of nitroethane, l-nitropropane, Z-nitropropane, l-nitrobutane, and l-nitroisobutane, and a monohydric aliphatic alcohol containing from 1 to 4 carbon atoms.

2. A composition. of matter comprising cellulose acetate having an acetyl number below 40, and a solvent mixture comprising a nitroparaflin chosen from the group consisting of nitroethane, l-nitropropane, 2-nitropropane, 'l-nitrobutane, and l-nitroisobutane, and a monohydric aliphatic alcohol containing from 1 to 4 carbon atoms, the components of the solvent mixture being in such proportion as to completely dissolve the cellulose acetate.

3. A coating composition comprising cellulose acetate having an acetyl number below 40, a nitroparaflin chosen from the group consisting of nitroethane, l-nitropropane, 2-nitropropane, 1- nitrobutane, and l-nitroisobutane, a monohydric aliphatic alcohol containing from 1 to 4 carbon atoms, and a hydrocarbon diluent, the solid and solvent components being of such character and in such relative amounts as to maintain the cellulose acetate in solution during evaporation of the solvent components to deposit a film.

HERBERT L. WAMPNER. CHARLES BOGIN.