Study On The Viscoelasticity Property Of The PVC Calendered Flexible Composites

As a newly arisen material, PVC calendered composites have been widely used in tenting, advertising banner, pool bottom, geo-textile field. It has great potential in the future markets. So the study on its properties is more and more important. In this paper, it mainly studied the Viscoelasticity properties of the PVC calendered composites by the static study methods.In this thesis, five samples were selected which were of different structures and different yarn count while using the same PET filament yarn and the same PVC as the raw material. Besides the tests of the weight per square meter, the yarn count, the thickness of the samples, the tests and the analysis for the tensile break property, the stress relaxation property and the creep property were as the main work. The mechanical model was established to simulate the stress relaxation and the creep property of flexible composites. A simple exchange method between the relaxation modulus and the creep modulus was also deducted.Several conclusions are got from the tensile break tests as below: The process of the calendering had great effect to the strength of final products; The yarn count of the reinforcement fabric and the thickness of the PVC also have obvious effect to the final flexible composites; In the warp knitted bi-axial fabric, the potential strength can be fully used as the yarns are flat without crimp, so the warp knitted fabric has better relaxation rate than other fabrics when they are as the reinforcement part.Through the analysis on the Lab test result of the stress relaxation, the five different reinforcement fabric samples all follow the normal regulation of the Viscoelasticity properties. And that, as the fixed tensile length increases, the relaxation stress increases, but the relaxation rate falls, meaning that the probability of the stress relaxation decrease.After the study on the test results of the long term creep, the factors which affect the creep property were concluded. On one hand, the flexible composite itself, the heat and strength history under the calendering process is as the main factor, if the reinforcement fabric was under proper strength during the calendering, it would have good property to resist the creep on the final flexible composite. On the other hand, the outer strain is another important factor, if the strain was large, the creep would be fierce, but this connection is of nonlinear.The Eyring model was used to imitate the stress relaxation and also the creep. The parameters of the 2 equations of Eyring model were calculated by a method called Matlab. The experimental results showed that the PVC calendered flexible composites fit the Eyring model very well in 10~4s, and what means that the PVC calendered flexible composites follow the nonlinear Viscoelasticity theory. Beside, a simple method to exchange the stress relaxation modulus and the creep modulus was deducted.In this thesis, however there are still some shortages to be improved in the future. At the end of the paper, a, sum-up was made and future development for the flexible composites was forecasted.Written by Zhu Yongyi(Textile Engineering)Supervised by Chen Nanliang...