CELLULOSE SHEET SWELLING Effect of Temperature and Concentration of Sodium Hydroxide Solutions GEORGE A. RICHTER AND KENNETH E. GLIDDEN Brown Company, Berlin, IC'. H. This article is the first of a series that deals with the behavior of sheeted cellulose fibers when immersed in solutions that cause the sheets to swell. The effects produced are measured primarily in terms of the three dimensional changes, the volume increase, and the weight increase of the drained sheet. This first article deals with five basically different types of fiber, four of wood origin, the other a normal grade of purified cotton linters. The data are concerned wholly with results obtained when the sheets are submerged i n sodium hydroxide solutions
that range in concentration from 6 to 30 per cent, at temperatures from 5" to 35" C. The data are expressed graphically and reveal marked differences i n the degree to which each type of sheet is swollen. The process history of the cellulose influences both weight increase and volume increase of the sheets i n question. In all cases the volumetric swelling and the absorption of liquor are maximum at concentrations of 10 to 12 per cent sodium hydroxide and are more pronounced at the lower temperatures. No attempt is made to explain the relations of cause and effect.
HEETS of interfelted cellulose fibers of different origin and type exhibit vastly different behavior when immersed in liquids that possess the power of swelling the individual fibers. Furthermore, the change in sheet dimensions that occurs when the sheet is submerged in swelling agent is greatly affected by the state of the liquid. Concentration and temperature play major roles in determining the degree to which the sheet swells and shrinks when immersed. As is evidenced by later data, a swelling medium, whether it be a solution or a simple reagent, almost invariably causes the sheet to expand greatly in thickness, and this increased thickness is accompanied by a shrinkage in lateral dimensions. The orientation of the individual fibers in the sheet plays an important part in determining the proportionate changes, especially in the lateral dimensions. Lateral shrinkages are much less in degree than is the increase in thickness-hence a marked increase in sheet volume. The swelling of individual fibers and the attendant pronounced increase in total volume of sheet when so treated form the basis of several important industrial processes. To illustrate, we may mention the manufacture of vulcanized paper and of parchment paper, and also that important step of steeping cellulose sheets in strong alkali preliminary to their conversion into the xanthate solutions. Investigators have given prolonged attention to the study of the behavior of the individual cellulose fiber, particularly when acted upon by strong alkaline aqueous solution, particularly in the case of cotton ( 1 , 4). This is not surprising when one bears in mind the earlier work of Mercer and the need of such knowledge in the mercerization of textiles. Later attention was directed to the wood cellulose fibers of different degrees of purity, and here the results are more confusing because of the wide difference in properties of such wood fibers,
depending not only upon origin but on the ways and means of isolating those fibers from the tree. As will be shown, wood fibers from the same species behave very differently in strong alkaline solutions, depending upon their process history. More recently some study has been given to the relations that exist between the history and properties of felted cellulose sheets and their behavior when immersed in the alkaline swelling agents under conditions that prevent a disintegration of the sheet into individualized fibers (3, 3, 5-8). Here are encountered additional variables that relate wholly to the physical structure and pattern of the sheet itself. The most comprehensive recent work is that of Jayme and Steinmann (6). These investigators define a unit (thickness swelling volume) which is the volume occupied by one gram of dry pulp when in the swollen stat'e, measured in sheet form and without regard to lateral shrinkage. They discuss the relation bet'ween degree of swelling and hydration, degree of beating, rate of attack by acids, adsorption of dyes and hydroxides, and t,he effect of other processing steps. In recent years similar investigations were initiated in the Brown Company's laboratories, where a wide variety of fibers are ayailable and where the sheet characteristics can be varied.
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Experimental Procedure
Sheets, fabricated for the most PHEP.
