Tprinciple of wet spinning process-Part 6 Thermodynamics of polymer dissolution process

Thermodynamics of polymer dissolution process

1) Molecular motion changes during polymer dissolution

Macromolecular intermolecular forces J,interaction between macromolecule and solvent f,the number of spatal arrangement states and kinematic degree of freedom of various molecules t.

2) Thermodynamic parameter changes during polymer dissolution

AFm<0 the dissolution process can occur spontaneously

AFm= AHm-TASm=Xi △ Hn+X2 A H22- A H12 ・XiT A Sn- X2T A s22+t △ S12

The change of prem during dissolution is increased,AS>0,SO the value of △Fm depends on the sum of △Hm.

3) The type of dissolution of polymers

Generally, according to the change of thermodynamic function of polymer - solvent system in the process of dissolution, it can be roughly divided into the following two types of dissolution.  

(A) process of dissolution determined by themal change

In these kinds of system the spedfic changes of the petocess of dissolution are very small compared wuth the themal changes,they can be igored.

ASm«0,and△ Fm= △ Hm= Xi A H11+X2 △ H22

△ H12 conditions for dissolution of polimers ：AFm<0,

Thant’s:|AH12|>|x1AH12+x2AH22l

characteristic：ASm«O, A Hm <0

Range of application:The dissolution process of polar polymer(especially those with rigid chains)occurs in polar solvents.Due to the strong interaction between macromolecules ,and solvent molecules,the dissolution process is exothermic(-hm<0),so that the free energy of the mixture system decreases(AFm<0)and the polymer dissolves.

(B) A dissolution process determined by precrystallization

In general,the dissolution of nonpolar polymers in nonpilar solvents falls into this category.There is no exothemic or endothemic effect(AHm>0).At the same time,the genus changes were very large(ASm>0)

Characteristics:△Sm»O, △HmNO

The above mentioned only general characteristics of the dissolution process of different type of system.In fact,the dissolution of polar polymers in polar solvents can also occur no heat or endothemic phenomenon,the situation is more conplex.