Swelling degree, definition

Both Qv(x) and Q°(x) decrease as the polymerization proceeds and, after a definite conversion Qv(x) may reach the value of Qx(x). Since the dilution of a gel cannot be greater than its equilibrium degree of swelling, the excess of solvent should separate from the gel phase resulting in the syneresis, i.e. in phase separation. The condition for incipient phase separation during copolymerization of divinyl/vinyl monomers is given by [107]... 

It is probable that varying degrees of ordering of chains exist in a cellulosic material and that a sharp differentiation of crystalline and non-crystalline celluloses may not be feasible or even possible. Theoretically, the lateral surfaces of crystallites are amorphous but may have far less importance in determining such properties as strength, flexibility and extensibility than the non-crystalline cellulose which supplies continuity of structure in the direction of crystallite orientation. Yet properties like moisture absorption and swelling may be more dependent upon the amount of cellulose which exceeds a certain degree of disorder (permeability) than upon location. The definition of crystallinity may, therefore, be made ultimately in terms of practical objectives. 

Under such conditions the theory held satisfactorily in various instances. Loeb, c. g., has shown that the osmotic pressure of a dilute protein solution in dependence on the hydrogen ion concentration, which shows a maximum value at a definite pH, satisfactorily conforms with the theory. If gelatin is allowed to swell in water and then submerged in dilute hydrochloric acid, the degree of swelling reaches a maximum at about the same pH. 

Several researchers working with hydrogels, especially for biomedical applications, prefer to use other similar parameters to define the equilibrium swelling behavior [28]. Another definition is that of the weight degree of swelling, q, which is the ratio of the weight of the swollen sample over that of the dry sample [9]. 

The TD variations are nearly totally due to die design. The first problem is to design a feed system that will distribute the melt uniformly to the shaping portion of the die. (See Fig. 7.4 for definition of parts of a die.) In the event this is not possible, then it must be possible to adjust the die lips in such a way that the fluid will leave the die with a uniform thickness. Part of the thickness variation in the TD is due to the inability to feed the die uniformly from the extmder, while the rest is due to the phenomenon of die swell. Since the degree of swell may vary nonuniformly over the cross section due to variations in the shear rate, the die lips (main shaping section) may have to be designed to compensate for this. 

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