Influence of temperature on the microstructure and mechanical properties of stretched polypropylene

cited By 2International audienceMicrostructure and mechanical properties of isotactic polypropylene (iPP) stretched at different temperatures were studied. Strain-induced fibrils were observed after stretching. Crystallinity (Xc), crystallite thickness (Lc), long period (Lpf), and diameter (Df) of fibrils were characterized by Differential Scanning Calorimetry and Small angle X-ray scattering. Lpf of stretched iPP below 60°C was found to be lower than undrawn iPP. Xc, Lc, and Df increased with increasing draw temperature. Tensile test showed that Young's moduli of stretched iPPs were negatively dependent on Xc and Lc. The fraction of taut tie molecules was estimated from the mechanical model. Results showed that more tie molecules were formed in the samples stretched at lower temperatures. Dynamical mechanical analysis showed that glass transition temperature was strongly dependent on the draw temperature. The glass transition peak disappeared in stretched iPPs obtained below 80°C. © 2015 Wiley Periodicals, Inc