A Study On The Crystallization Behavior And Morphologies Of Poly(Ethylene Adipate)

In this study,the crystallization and morphologies of poly(ethylene adipate)(PEA)were studied by polarized optical microscopy(POM),transmission electron microscopy(TEM),wide/small-angle X-ray diffraction(WAXD/SAXS),and atomic force microscopy(AFM).It was found that PEA can form ring-banded spherulites when crystallized at a narrow temperature range.WAXS results indicated that PEA moleculer only aligns into monoclinic unit cell when crystallizing from the melt.Then highly-oriented PE substrate was used for PEA epitaxial crystallzation.Results showed that the folding plane of PEA moleculer is consistently the(110)plane,which means that main-chain tilting is common in PEA crystals regardless of the crystallization temperature.Thus,chain-tilting is not the essential origin for lamellar twisting.The observations of the trans-crystals of PEA induced by PE boundary shows that the distribution of unbalanced surface stress on lamellar opposite sides is actually the key factor that renders PEA lamellar with different deformation——twisting,curvature,and bending.When observed under crossed polarizer with a complementary plate,PEA spherulites prepared at different temperature or within different sample thickness displayed complex birefringence.In thin films(300 nm),edge-on lamellae dominates the whole spherulite because of the homogeneous nucleation behavior at higher supercooling,rendering PEA spherulites with negative birefringence;whereas low supercooling leads to heterogeneous nucleation with the subsequent formation of flat-on lamellae,showing positive birefringence.In thicker films(1000 nm),the coexistence of homogeneous and heterogeneous nucleation results in the formation of both edge-on and flat-on lamellae in a spherulite,and the various shapes of edge-on lamellae render different types of birefringence?Moreover,the thermal evaluation of PEA crystals shows that PEA banding structure has higher melting point than PEA crystals obtained at even higher temperature.In-situ AFM and SAXS were used to investigate this abnormal melting behavior of PEA crystals.Conbined with theoretical computation,it be explained that the amorphous region in PEA crystals plays a significant role in the melting behavior of PEA crystals.