Macromolecules, Vol.50, No.13, 5098-5106, 2017
Temperature-Dependent Alternating alpha- or beta-Transcrystalline Layers in Coextruded Isotactic Polypropylene Multilayered Films
Continuous and orderly alpha- or beta-transcrystallinity plays a significant role in achieving excellent performance for isotactic polypropylene (iPP). However, this special structure is difficult to obtain through conventional methods. Here, continuous and orderly alpha- or beta-transcrystallinity was constructed in an iPP layer of an eight-layer iPP/alpha-iPP sample using a layered design and temperature control. The crystalline structure and morphology of the iPP layer were greatly influenced by the cooling rate. The iPP layer contained a large amount of beta-transcrystallinity and a small amount of alpha-transcrystallinity when the sample was cooled to 130 degrees C for isothermal crystallization at a cooling rate of 50 degrees C/min. However, only a-transcrystallinity was formed in the iPP layer when the cooling rate was 1 degrees C/min. The different crystallization mechanisms are discussed in this paper. In addition, the experimental results showed that beta-transcrystallinity could simultaneously improve both the tensile and impact properties.