Effect of heat treatment on structure and properties of PET BSY

The length-wise structure,boiling water shrinkage and tensile properties of bi-shrinkage yarns (BSY) are examined before and after boiling water treatment.The bi-shrinkage yarns (BSY) is composed of preorientted yarn (POY) /fully drawn yarn (FDY) which is produced by one-step spinning process.The results show that the high-shrinkage yarn FDY constructs the skeleton of BSY,and the lowshrinkage POY forms filament loops on the surface of BSY.There are two peaks in tensile curves of BSY,which means that the two components do not break at the same time,FDY breaks firstly,and then POY.BSY breaking processes are different before and after being treated in boiling water.The breaking tenacity of BSY is mainly determined by FDY,and the initial modulus of BSY is mainly determined by POY.