Swelling of cellulose

Hysteresis is observed not only in the sorption isotherms but also in calorimetric measurements of heat of wetting at different moisture contents, and it is thus a combined entropy and enthalpy phenomenon. A reliable explanation for this effect is not currently available, but there is speculation that it is due to the stresses which are induced as the cellulose swells. Since the swelling of cellulose is not completely reversible, mechanical recovery is incomplete and hysteresis will therefore be present both in the internal stress-strain curve of the sample, and also in the water adsorption isotherm. 

Table 23. Polymerization of acrylonitrile by swelling of cellulose acetate vapor (80)...

Fig. 116. Diagram by Trogus [5] /—Formation of the addition (Knecht) compounds, //—Nitrationjof cellulose (in % N), ///—Freezing temperatureof HNO3-H2O solutions, IV— Partial vapour pressure of HNO3 in aqueous nitric acid. Hatched area — strong swelling of cellulose fibre. Cross hatched area — solution of cellulose fibre...

Staudinger, H., and T. Eicher On the swelling of cellulose, and the inclusion of cellulose with fatty acids of low molecular weight. Makromol. Chem. 10, 254 (1953). 

Staudinger, "Die Hochmolekularen Organischen Verbindungen, Kautschuk und Cellulose , Springer, Berlin(1960) 58)Consultants Bureau Interprises Inc, Soviet Research on the Swelling of Cellulose Materials, 1949 1956 , English Translation, NY(1960) 59)J.P.Casey,... 

Zeronian, S. H. Intercrystalline swelling of cellulose in Cellulose chemistry and its applications Nevell, T. P. Zeronian, S. H., Eds. John Wiley Sons New York, 1985,... 

Zeronian, S.H., Intercrystalline swelling of cellulose, in Cellulose Chemistry and Its Applications, Nevell, T.P. and Zeronian, S.H., Eds., Ellis Horwood Ltd., Chichester, England and Halsted Press,... 

The swelling of cellulosic fibres by moisture can be reduced by the application of self crosslinking urea or melamine products as well as by products that mainly crosslink with cellulose molecules. Without such a crosslinking finish, cellulose fibres can take up more than 10 % of their weight in water. As the fibres swell, the fabric must crease and shrink to relieve the internal stresses caused by the swelling. 

Table 8. Sorption of iodine and heats of swelling of cellulose and mixed polysaccharide (III) in water...

Solvation and swelling of cellulosic polymers possible effect of H bonding,... 

Swelling of cellulose fibres in alkali increases with a decrease in temperature [17] as the formation of alkali-cellulose compounds is an exothermic process. At 0 C the swelling of cellulose in alkali (8-9% by weight) is about 800% (Fig. 9-1) and swelling decreases rapidly at higher concentration of alkali due to the decrystallisation of NaOH hydrates. The extent of swelling also decreases as the... 

Vermaas D, Hermans JJ. The swelling of cellulose xanthate gels in dilute salt solutions. Recueil 1948 67 983-997. 

K—Partial vapour pressure of HNO3 in aqueous nitric acid. Hatched area — strong swelling of cellulose fibre. Cross hatched area — solution of cellulose fibre... 

Water-soluble (uncrosslinked) polymers absorb water, swell and concomitantly dissolve (erode). Not much has been published on water penetration kinetics and swelling of cellulose derivatives. Wan and Prasad [74] studied the linear swelling of MC films at 34,37 and 40 °C. Concurrently, they were able to explain the slow disintegration of pharmaceutical tablets prepared using this binder at low temperature by the higher degree of swelling. 

The complex-formation of polysaccharides with alkali metals and alkaline-earth metals has already been discussed in this Series. A dextran-iron complex has been used in the experimental therapy of synovitis, and chondroitin sulfate-iron colloids have been prepared. The swelling of cellulose in aqueous solutions of zinc chloride depends on the formation of a complex with the vicinal 2- and 3- hydroxyl groups of the repeating unit. ... 

II allomorph is known by the term regenerated cellulose. Regeneration involves either preparing a solution of cellulose in an appropriate solvent or of an intermediate derivative followed by coagulation and recrystallization. This process is used to produce rayon fibers. Mercerization involves intracrystalline swelling of cellulose in concentrated aqueous sodium hydroxide (NaOH), followed by washing and recrystallization. This process is used to improve the properties of natural yams and fabrics. The transition from cellulose I to cellulose II is not reversible, and fliis implies that cellulose II is a stable form as compared with the metastable cellulose I. 

The swelling of cellulose in the presence of moisture is a well known property of this material. Other protic and nonprotic solvents such as methanol, ethanol, acetonitrile, and acetone also have the capacity to swell microcrystalline cellulose. However, solvents such as benzene, toluene, or dichloromethane do not promote this effect. Therefore it is possible to control adsorption of probes on microcrystalline cellulose, either on the surface or entrapped within the natural polymer chains. After the removal of the solvent used for sample preparation, and for a swelling solvent, a chain-guest-chain interaction is promoted, replacing the previous chain-solvent-chain interaction. 

In commercial practice, pulp is steeped (soaked) in aqueous sodium hydroxide of about 18% concentration at ambient or slightly higher temperature ( 25°C). Because swelling of cellulose is temperature-dependent, less caustic is used at lower temperatures and more at higher... 

Neale endeavoured to explain the swelling of cellulose in sodium hydroxide solutions (which shows a marked maximum at a concentration of about 2 mole/liter) on the basis of the Donnan theory, thereby considering cellulose as a weak acid capable of splitting off hydrogen ions. Though the results were consistent with the experimental data, the behaviour of this system seems to require another explanation, since Hess and coworkers have shown that the results of experiments on the distribution of added neutral salts lead to the conclusion that the theory does not hold. Moreover, the assumption that cellulose acts as a weak acid seems not to be sufficiently justified. It is true that carboxylic endgroups frequently occur in cellulose, but these cannot be held responsible for the acid character postulated by Neale, since they have a much larger dissociation constant than the one required by Neale s theory. 

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