The melting behavior

crystallizing characteristics and tensile properties of biaxially oriented polypropylene (PP homopolymer for BOPP film (h-BOPP) and PP-PE copolymer for BOPP film (c-BOPP)) were investigated by differential scanning calorimetry (DSC)

optical microscopy (OM)

tensile test and wide angle X-ray diffraction (WAXD).The results showed that compared with h-BOPP

the isotacticity and crystallization rate of c-BOPP were lower

and its half crystallization time was longer at the same crystallization temperature.For h-BOPP and c-BOPP samples without annealing

the elongation at break was higher.However

after annealing at 140 ℃ for 2 h

the elongation at break of both h-BOPP and c-BOPP decreased a lot

as the more perfect crystallites formed.It was believed that crystals of higher perfection had less ability to rearrange themselves under stretching and therefore could not sustain large extensional deformation.Since there are many ethylene segments in the molecular chains that could inhibit the nucleation and crystallization

the crystallization rate of c-BOPP was low

resulting in lower perfect crystallites after annealing.So the elongation at break of c-BOPP was a little more than that of h-BOPP.In addition

the crystalline structure was proven to be partially destroyed under the extensional deformation

and the oriented noncrystalline molecular chains could be easily reorganized into more perfect crystals in the post heating runs.Due to the ethylene segments in the molecular chains of h-BOPP

the oriented noncrystalline molecular chains of h-BOPP could be easier reorganized.This paper explained the mechanism related to the differences between the tensile properties and crystallization behavior of BOPP with different molecular chains.