Extrusion cast poly(lactic acid) (PLA) films were stretched uniaxially in the rubbery state while their optical and mechanical behavior were monitored with our on-line stretch birefringence instrumentation. If the films are stretched fast they exhibit nematic order as also reflected in the negative deviation from linearity in stress optical behavior. This structure was found to eventually convert to oriented ?-phase crystalline form if sufficiently long time is allowed for relaxation If, on the other hand, a rapid slight retraction is employed, this conversion form nematic order oriented crystalline order is accelerated. This significant behavior strongly supports the use of retraction stages in processes that utilize uniaxial and biaxial stretching.
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