Influence of annealing on the polycarbonate stretching process

Abstract

Uniaxial stretching generates self-reinforcement in polycarbonate. This self-reinforcement is due to an increase in the strength and modulus of elasticity brought about by a mutually supporting molecular structure; it is a function of the stretching ratio, the stretching rate, the stretching temperature and the annealing temperature. The film undergoes annealing as a result of the stretching process. This reduces the strain-induced stress over time. The reduction in stress results from the relaxation of orientated and stretched molecular chains, which return to their initial state. This process is temperature and time-dependent: the higher the temperature, the higher the flexibility of the molecules will be, and the more readily the molecules will deform. The longer the deformation time, the more extensive the rearrangement of the molecular chains will be. The relaxation time can be used as an indicator for characterizing the time required for rearrangement. During stretching on the monoaxial stretching line, it is clear that annealing at a lower stretching ratio and orientation will lead to a higher capacity for relaxation, as with a higher stretching ratio. The annealing time increases as the stretching rate falls, and hence more time is available for molecular deformation. Similarly, with a constant stretching ratio: the lower the stretching rate, the longer the annealing time and the higher the relaxation capacity will be. © 2014 American Institute of Physics.