Electrospinning Nanofibers And Crystallization Properties Of Polybutene-1

This paper systematically studied the solution electrospinning and crystalline properties of highly isotactic polybutene-1(PB-1), explored the suitable solvent for electrospinning and the influence of electrospinning parameters on the fiber morphology as well as the crystalline transformation of electrospun membrane in different annealing temperature, and then discussed the crystalline transformation process in different solvent vapor of polybutene-1 hot-pressed film, electrospun membrane and solution cast film, meanwhile the transformation mechanism of polybutene-1 from form II to form I also be proposed.The electrospinning solvent system and parameters of polybutene-1 electrospinning has been investigated. The results showed that with the increase of solution concentration and syringe rate, the bead-like morphology decreased, fiber diameter and distribution increased. With the increase of voltage, the electrospun process varied from no fiber to stable electrospining and the fiber diameter decreased first and then increased, on the other hand the distribution of fiber diameter broadened in higher voltage. The suitable electrospinning solvent system was cyclohexane: N, N-dimethyl acetamide(DMAc) =9:1(v:v), PB-1 solution concentration was 4%~6% g/m L, voltage was 15~30 k V and syringe rate was 40~60 ?L/min. The initial crystal form of electrospun membrane was form II and form I, high temperature annealing significantly promoted the crystal transformation from crystal form II to crystal form I. Electrospun membrane obtained at 25 oC possessed of higher initial form I content than 40 oC.The effect of different solvent vapor annealing on polymorphic transformation in both hot-pressed film, electrospun nonwoven and solution cast film of isotactic polybutene-1(PB-1) indicated that chloroform and water vapor has accelerated crystal transformation from form II to form I of hot-pressed film and electrospun membrane, especially in chloroform atmosphere. The total crystalline content(HI+II) of hot-pressed film showed an increased tendency while reverse tendency for electrospun membrane with the annealing time. In contrast, a mixture of form III and a small amount of form I' obtained in solution cast film and all crystalline content fluctuated in a fixed value with solvent vapor annealing.Effect of the annealing temperature on the transformation from form II to form I of PB-1 during water vapor annealing showed a lower t1/2 in high temperature than low temperature which demonstrated that high temperature water vapor annealing promoted polymorphic transformation. The transformation process of form II to form I in different air and water vapor annealing temperature showed that a faster transformation rate in high temperature presented in earlier stage, however, the residual portion of form II under high temperature in the later stage which suggested that random nucleation of crystal I has been restricted. Thus we proposed that the formation of crystal form I included crystal nucleation and growth which controlled by thermal thermodynamics, and earlier transformation process is dominant.To verify the nucleation process, nucleating agent with different proportion has been added to PB-1. The results further demonstrated that the decisive stage of crystal transformation from form II to crystal form I was mainly situated in the nucleation process in the earlier stage which was supplemented by later random nucleation process. Meanwhile, the amorphous region had an equivalent effects on the formation of crystal form I.