Relative Humidity On The Uniaxial Stretching Of Poly (ethylene Terephthalate) Fiber Structure Evolution Of The Role

In this paper, the influence of relative humidity on cold crystallization behavior of uniaxially oriented PET fibers was investigated by using DSC method with a constant heating rate. The condition of the heat treatment was established through the DSC curves. The equatorial and meridional wide-angle X-ray diffraction of the sample was carried out. An nonisothermal equation was used for kinetics analysis of the crystallization progress by the least squares method.First, the as-spun PET fibers were used to prepare the oriented PET fibers with different degree of orientation. And then they were stored under different relative humidity which was controlled through saturation solution of different salts. Many tests were carried out on the oriented PET fibers. By the test of the moisture regain, the moisture regain of the fibers increase with raising the relative humidity. Through the degree of orientation of the PET fibers, it was found that the degree of orientation of the uniaxially oriented fibers increases with draw ratio at a certain humidity. When the environment humidity is between 0%RH~50%RH, the degree of orientation of the fibers with draw ratio at 2.48, 3.30 and 3.91 is trending down with the increasing of degree of orientation. When the environment humidity is between 50%RH~ 100%RH, the degree of orientation of the fibers with the draw ratio at 2.48, 3.30 and 3.91 is trending up with the increasing of degree of orientation. The fibers with draw ratio at 1.75 are trending down through the whole humidity region. The DSC curve with constant heating of the sample stored under the 0%RH indicates that the cold crystallization peaks of the highly oriented fibers become very dispersive and spread to the lower temperature. The DSC curve with constant heating of the sample stored under different varies relative humidity shows that the glass transition temperature (T_g) shifts toward a lower temperature and the cold crystallization temperature (T_c) extends to the low temperature with increasing the relative humidity. And the cold crystallization divided into two small peaks. During the WAXD test, the condition for preparing PET fibers with orientation but no obviously crystallization was found.The model of cold crystallization of the PET fibers was proposed. Through the kinetics analysis of the PET fibers, the influence of the water molecule on the crystallization process was found. When the environment humidity is between 0~22.5%RH, water molecules act as plasticizer. When the environment humidity is between 22.5~100%RH, water molecules seduce segment arrange in order. And the segment become potential crystallsite of sporadic nucleation. When heating treatment the probability of the sporadic nucleation is increases.