Shear Effects On Crystallization Behaviors And Structures Of Isotactic Poly-1-butene

Isotactic poly-1-butene has good thermal-barrier properties. It is widely used in asfeed-pipe material for hot water pipes. But its structures and properties will beaffected by flow field during processing operations. Research on the crystallizationbehaviors and structures of poly-1-butene subjected to shear is of great importance.In this study we use optical microscopy to study the morphology and growth rateof i-PB during isothermal crystallization. Under shear conditions the nucleationdensity is higher and rod-like structures aligned in the direction of shear flow. In lowshear rate range the growth rate of sphero-crystal increase with increasing shear rate.When the shear rate is0.5s-1shear time is5s, after isothermal crystallization at95℃, we use XRD to track the phase transformation rate of i-PB and find that it is notaffected by shear flow.Further we discuss the changes in lamellae and crystallite structure on sampleswhich have completed transformation. The degree of orientation increases with theincreasing of shear rate. The long period and crystallize layer thickness along themeridian are not affected by shear flow, the long period along the equator increaseslightly due to thicken of crystallize layer. The lattice spacing decrease with theincreasing shear rate, which implied that shear can induce a close package of chains.As the shear time increases the long period along the meridian do not change, the longperiod along the equator increase slightly. And the lattice spacing change slightly. Asthe shear temperature increases the orientation function of shear flow decreased, thewhole system is more approach to the static isothermal crystallization.