Influence of Moisture Sorption and Other Pretreatments on the Acetylation of Cotton with Acetic Anhydride and Pyridine

Abstract

TWO different methods have been used for the partial acetylation of cellulose. One of these, acidcatalyzed acetylation, has been the subject of numerous reports [2 through 5, 7, 8, 15, 17, 19] establishing the influence of pretreatments and conditions of reaction in the production of partially acetylated cotton. The other, reaction with acetic anhydride in the presence of pyridine [10], has received less attention. The limited investigations of this reaction which have been reported [1, 9 through 11, 14, 18] indicate the importance of swelling agents in increasing the reactivity of cellulose. However, the influence of moisture sorption and other pretreatments on the acetylation of cotton with acetic anhydride and pyridine has not been systematically investigated.In order to obtain such information, the effect of moisture content and previous sorption history on the extent of acetylation under a selected set of conditions have been studied. The increased reactivity of dried cotton, due to pretreatment with agents other than water, and the reversibility on drying of the eff ect of treatment with sodium hydroxide, a swelling agent which penetrates the crystalline regions, has also been investigated.In his discussion of cellulose reactions, Heuser [12] concluded that acetylation is a reaction which exhibits no marked preference for either the primary or secondary hydroxyl groups of cellulose. However, in order for reaction to take place, the reagent must penetrate to the hydroxyl groups. Consequently, the rate of acetylation (or the extent of reaction under certain arbitrary conditions) is a function of the submicroscopic structure. When cellulose absorbs, water swelling occurs as the water penetrates the intermicellar spaces, and the accessibility of the hydroxyl groups to chemical reaction is increased. In order to obtain penetration into the intramicellar spaces, alkalis, organic bases, or other strong swelling agents are required. Whether regarded as amorphous and crystalline or accessible and inaccessible, the duality of submicroscopic structure of cellulose plays an important role in the acetylation of cotton. As a result, changes in reactivity toward acetylation may be regarded as a reflection of changes in the submicroscopic structure of cotton. Moisture SorptionEmpire, Stoneville 2B, and Rowden 41B cottons were selected to obtain specimens differing in maturity and fineness (Table I ) . In addition to acetylation of all three raw cottons, the first two were acetylated after purification by successive extraction with hot alcohol and boiling in 1% alkali [13]. The cotton samples were brought to the absorbing side of the moisture sorption cycle by drying them in an oven at 110° C. for 16 hr. and then conditioning them at suitable relative humidities until they had reached the desired moisture contents.The desorbing cottons were prepared by

Cellulose Swelling Measured by Benzene Retention

“…The slow and limited swelling of the dry mercerized fiber in acetic acid, a classic example, suggests that in the amorphous region of such fiber many chains are in closer proximity and possess stronger cross 1 Present address, 28 Monroe Ave., Pittsford, N. Y. bonds than in the unmercerized cotton itself.…”

Influence of Pretreatment on the Reactivity of Cotton as Measured by Acetylation

“…Sodium hydroxide and trimethylbt>nzyl ammonium hydroxide, Triton 11,2 were used as catalysts, but other strong bases could probably be used. 1 One of the laboratories of the Southern Utilization Research Branch, Agricultural Research Service, U.S. Department of Agriculture. 2 It is not the policy of the Department to recommend the products of one company over those of any others engaged in the same business.…”

Part II: Effecta on Chemical Modification

“…IT IS known that 2-thiobarbituric acid (TBA) forms color compounds when heated in acidic solution with deteriorated lipids [2,4,6,8,11,13, 16], lignin [3], milk [6,9,14] or lactose irradiated with cathode rays [15]. These color compounds in acidic solutions exhibit absorption in the region of visible light at a wavelength dependent upon the material tested.…”