Temperature-dependent Lamellae Structure in Stretch-oriented Isotactic Polypropylene
In this work,the working roles of stretching temperature(Ts)on impacting the microstructure characteristics of oriented isotactic polypropylene(iPP)were surveyed in depth by a combination of two-dimentional wide-angle/small-angle X-ray scattering,differential scanning calorimetry,dynamic mechanical analysis,etc.The results show that the initial spherulitic morphology transformed into the fibrillar crystal morphology after experiencing hot-stretching process,and that the crystalline fibrils consist of the altermative stacks of highly orentied lamellae and amorphous layers.A Ts-dominant crystallization enhancement.was found as that:crystallinity and mean lamellar thickness increased monotonously as elevating Ts.Meanwhile,as the Ts increases,the physical properties of the crystalline phase begin to diverge significantly from those of the amorphous phase,resulting in opposite trends for chain relaxation in the two phases.Two fractions of lamellae with different thicknesses(melt point)are newly formed during the hot stretching process.The lamellae with higher melt point are arisen from the melt-recrystallization mechansim,while the occurrence of low-melt point lamellae obeys the strain-induced crystallization mechanism.This work provides a new understanding into the rule of structural manipulation of semicrystalline polymers during stretch processing.
Isotactic polypropyleneStretching temperatureLamellaeCrystallinityMelt point
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