True Stress,True Strain and Real Time Birefringence Development of Orientation in Natural Rubber during Uniaxial Stretching as Detected by Spectral Birefringence Technique

摘要

We have developed a real-time measuring system to analyze the molecular orientation and its mechanical response during uniaxial deformation with automated spectral birefringence technique.This instrument allows simultaneous recording of force,sample width,optical retardation and strain during uniaxial deformation.The automated spectral birefringence system was found to be sensitive enough to follow the small changes in retardation in the natural rubber due to its low intrinsic birefringence.This data is then converted to real time birefringence through on-line measurement of thickness through laser detection system.The real time determination of true stress- true strain -birefringence data allows for fundamental understanding of the response of polymer chains to mechanical deformation.The molecular responses of uniaxial stretching,stress relaxation and hysteresis loss (stretching and retraction) were studied.The data indicates that chain orientation is a linear function of deformation.The stress- induced crystallization occurs at high deformation levels as expected.The stress-induced crystallization was found to be a direct consequence of hysteresis loss.True stress - optical and true strain -optical coefficients are discussed.