Analysis of the tensile modulus of poly(p-hydroxybenzoate)/poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) ternary polyester composite fibers

摘要

Liquid crystalline polymer reinforced plastics were prepared by compounding (PHB/PEN/PET) blends. A fibrillar PHB structure was formed in situ in the PEN/PET matrix under a high elongational flow field during melt-spinning of th ecomposite fibers. The fomation of PHB microfibrils in the composite fiber with different PHB contents and winding speeds was observed. The PHB microfibril reinforced PEN/PET composite fibers exhibited an unexpectedly low tensile modulus. We have evaluated the tensile modulus of the fibers using the non-modified~22 and a modified~23 Halpin-Tsai model. From the analysis of both models, large differences were found vbetween the theoretical and experimental values of the tensile modulus, and the low value of the tensile modulus of the composite fiber could not adequately be explained by either model. Thus, we analyzed the observed modulus values using the Takayanagi model,~24 which describes the concept of mechanical discontinuities in semi-crystalline polymers. Using the Takayanagi model, the effective fraction of continuous or discontinuous microfibrils was evaluated. Consequently, we could successfully explain the very low modulus of the PHB/PEN/PET composite fiber, having a large number of PHB microfibris, using the Takayanagi model.