拉伸过程中聚偏氟乙烯纤维晶体结构变化

Crystalline Structure Changes of Poly (vinylidene fluoride) Fibers during Stretching Process

采用熔融纺丝法制备不同喷丝头拉伸比聚偏氟乙烯(PVDF)初生纤维,再经后拉伸制得不同后拉伸比PVDF纤维.对纤维在不同拉伸过程中晶体结构研究表明:随喷丝头拉伸比增大,纤维结晶度、α晶型取向、大分子取向均增加,且喷丝头拉伸比达到一定程度后,变化更显著;而随后拉伸比增大,纤维结晶度无显著变化,但后拉伸较喷丝头拉伸更有利于α晶型向β晶型转变,且后拉伸比越高越易形成β晶型,当后拉伸使纤维进入直径均匀变小阶段后,β晶型取向效果更明显;后拉伸比为11时,β晶型含量达82.85%,β(110/200)晶面取向因子达0.83.

The poly(vinylidene fluoride)(PVDF)as-spun fibers with different spin-stretching ratios were fabricated via melt-spinning method using plunger spinning machine.PVDF fibers with different post-stretching ratios were subsequently obtained by post-stretching method under the thermal treatment condition.The crystal and orientation structure of the fibers were investigated by X-ray diffraction(XRD),differential scanning calorimetry(DSC),polarizing optical microscopy(POM)and so on.The results indicated the orientation ofαcrystal and macromolecular increased with the increasing spin-stretching ratio.Furthermore,as the higher spinstretching ratio increased,the degree of crystallinity of as-spun fiber was prone to perfection.Furthermore,according to the POM photomicrograph,the horizon of extinction position was almost entirely black,and the horizon of diagonal position was getting brighter,due to the increase of the anisotropy of as-spun fibers.This was attributed that the irregular fiber macromolecules were stretched to regular structure.When spin-stretching ratio was 330,the crystallinity of as-spun fiber could reach 56.38%and the orientation factor ofα(110/200)crystal plane was up to 0.89.In terms of post-stretching technique,the stretching ratios had no significant influence on the degree of crystallinity.However,the post-stretching process played a positive role in the transition of the crystal phase fromαtoβ.The molecular chains of the fibers are easier to slip and arrange regularly along the fiber axis during spin-stretching process.The conformation was easier to transfer fromαphase toβphase owing to the segmental motion of molecular chains during post-stretching process.Especially,the orientation ofβcrystal was also improved at the same time.Specially,when the post-stretching was up to the stage of uniform reduction of fiber diameter,the orientation ofβcrystal retained a high level.When post-stretching ratio was 11,the content ofβcrystal could account for 82.85%and the orientation factor ofβ(110/200)crystal plane was up to 0.83.