Swelling, influencing factors

The influence factors of SPNR/PSf ratio on swelling ratio of blend were investigated as shown in Figure 13.29. The lowest swelling ratio of the polymer blend was observed at 40/60 SPNR/PSf. 

Table 2 Factors Influencing Swelling of pH-Sensitive Hydrogels... 

In the manufacture of nitrocellulose powders the water is displaced with alcohol. This method was proposed by Lundholm and Sayers [3] and widely used in many countries [4, 5]. Despite the simplicity of the idea the dehydration process is rather complicated. It is influenced by such factors as the solubility of nitrocellulose in alcohol and the ability of nitrocellulose to swell under the influence of alcohol the lower the solubility of nitrocellulose in alcohol, the more easy dehydrated with alcohol. Since, however, the solubility of nitrocellulose depends primarily on its nitrogen content dehydration is easier with the higher nitrated types of nitrocellulose. 

We present a review of theoretical and experimental results on the swelling behavior and collapse transition in polymer gels obtained by our group at Moscow State University. The main attention is paid to polyelectrolyte networks where the most important factor is additional osmotic pressure created by mobile counter ions. The influence of other factors such as condensation of counter ions, external mechanical force, the mixed nature of low-molecular solvents, interaction of network chains with linear macromolecules and surfactants etc. is also taken into account Experimental results demonstrate a good correlation with theoretical analysis. 

Finally Papkov [52] observed that the surface tension of the solvent is a further factor influencing the solubility of cellulose esters. This worker established that the best solvents from a series of liquids resembling each other chemically, e.g. in a homologous range, were characterized by a moderate, optimum surface tension. Liquids having higher or lower surface tensions than this optimum value are worse solvents. The rule is also valid for mixtures. Thus a 50 50 acetone-water solution with a surface tension a = 30.4 dyne/cm caused only a weak swelling of... 

---