Cellulose nitrate, dilution ratio

If a non-solvent is added dropwise to a cellulose nitrate solution, the cellulose nitrate eventually separates as a precipitate or gel. The volumetric ratio of non-solvent to solvent that is still tolerated in the solution is termed the dilution ratio. The dilution ratio is an empirical, dimensionless quantity that provides information on the solvency of a solvent or solvent mixture. In order to determine the dilution ratio toluene or butanol is used as diluent (non-solvent). 

Mixtures of two solvents frequently have a higher dilution ratio than the pure components ether-alcohol and toluene ethanol mixtures are better solvents for cellulose nitrate than any of the pure solvents ethyl acetate and butyl acetate are... 

As expected, the dilution ratio falls with rising cellulose nitrate concentration in the solution (Table 8). 

The dilution ratio reveals some similarities between the solvency of different solvents. However, most measurements are restricted to cellulose nitrate, and extrapolation of the results to other binders seldom provides correct results. Furthermore the dilution ratios, unlike solubility parameters, are unable to explain several phenomena (e.g., the enhancement of the solvency of a solvent produced on adding a non-solvent). 

Table 7. Dependence of the dilution ratio on temperature (solute = cellulose nitrate diluent = toluene)...

Tables. Concentration dependence of the dilution ratio of cellulose nitrate solutions in butyl acetate ...

Cellulose nitrate, g Butyl acetate, mL Toluene, mL Dilution ratio... 

Table 13.6 Dilution ratio for a solution of cellulose nitrate in toluene...

The dilution ratio is the maximum number of units of diluent that can be added to unit volume of solvent before precipitation occurs. Cellulose nitrate dissolved in an oxygenated solvent (8 wt% resin) is the most classical method to determine dilution ratio used to evaluate toluene as a standard diluent and to compare different diluents and solvents with a standard solvent (n-butyl acetate). The standard dilution ratio of toluene by n-butyl acetate... 

ASTM D 1720-96. Standard test method for dilution ratio of active solvents in cellulose nitrate solutions. ASTM D 5062-96. Standard test method for resin solution dilutabihty by volumetric/gravimetric... 

The dilution ratio (ASTM D 1720) is a measure of solvent power of oxygenated solvents in relation to cellulose nitrate, although it can, in principle, also be obtained for other resins. The dilution ratio is a direct measure of the tolerance of a good or true solvent which contains a dissolved resin to a poor solvent or diluent added to it. ASTM D 1720 defines the maximum number of unit volumes of a diluent (e.g. toluene, xylene, SBP, /z-butanol) that can be added to a unit volume of the solvent under investigation to cause the... 

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