Solid-state shearing was applied on recycled poly(ethylene terephtalate) (PET) using twin-screw extruder. The shearing effect on isothermal crystallization was investigated by DSC. Structure formation in melt spinning was also studied by characterizing the spun fibers. It was found that the solid-state shearing imposes a great influence on its crystallization behavior. Crystallization peak temperature of the sheared PET (199 degrees C) was much higher than that of the PET without shearing (188 degrees C). Overall isothermal crystallization rate was found to be accelerated to more than 50 times by the shearing. The shearing effect remained even after fiber spinning (melt processing). Differences in crystallization behavior, fiber structure formation, and tensile properties of the fibers were found. (c) 2007 Wiley Periodicals, Inc.