Mechanical properties of poly(ethylene terephthalate) estimated in terms of orientation distribution of crystallites and amorphous chain segments under simultaneous biaxially stretching

Abstract

Young's modulus of poly(ethylene terephthalate) (PET) film was estimated by using the generalized orientation factors of crystallites and amorphous chain segments calculated from the orientation functions of crystallites and amorphous chain segments. Theoretical analysis was carried out on the basis of a two-phase model assuring the homogeneous stress hypothesis for a polycrystalline material. In this model system, the anisotropic crystal phase is surrounded by the anisotropic amorphous phase. As the theoretical values of elastic compliance of crystal unit of PET, the values by Tashiro were adopted. The experimental values of Young's modulus at room temperature were in good agreement with the predicted value calculated by using the theoretical compliance. Furthermore, the ultimate value of Young's modulus was estimated by assuming an ideal simultaneous biaxially stretching film with 100% crystallinity and the perfect orientation of the c-axis as well as that of benzene rings parallel to the film surface. The predicted ultimate goal of the Young's modulus was less than 5 GPa Indicating the difficulty in producing high modulus and high strength PET sheets in terms of theoretical aspects.