Annealing of drawn crystalline polymers

Abstract The annealing of drawn samples mobilizes the almost fully extended amorphous tie molecules which try to assume the thermodynamically required random conformations. The sample shrinks if annealed with free ends which permits the crystal blocks on different microfibrils and connected by almost fully extended taut tie molecules to move towards the position they had before plastic deformation. Hence the annealed sample has irretrievably lost most of its high axial elastic modulus which in the sample as drawn was caused by the high fraction of taut tie molecules. With fixed ends no shrinkage is possible so that the partial relaxation of interfibrillar taut tie molecules still lets them connect far away blocks. If their fraction is large enough so that in spite of the high surface to volume ratio which drastically depresses the crystallization temperature they can crystallize they do so after cooling to room temperature. The new axial crystalline bridges restore the high elastic modulus of the material before annealing, partially stabilize the sample against shrinkage during a new annealing, but also cause the dead bend effect which is the consequence of the replacement of flexible taut tie molecules in still amorphous conformation by rigid crystalline bridges. The drawing or extrusion at high temperature produces some annealing effects comparable with those of cold drawn material annealed with fixed ends.