| With the continuous development of PVC-Coated membrane material, it is widely used in theexhibitions, sports, transportation and recreation for outdoor construction work nowadays, becauseof its unique space structure, low price, low energy loss and excellent performance.The researchfrom many scholars showed that the ultraviolet rays from sunlight directly caused the degradationof PVC-Coated membrane material. The mechanical stresses could cause a change of the materialinternal physical and chemical structure, and altered the material aging speed, damaged thematerial strength and shortened the aging time. Eventually, it will lead to the performance loss ofthe membrane materials. In this thesis, the weathering performance of PVC-coated membranematerial under different tensile stresses were studied.The photo-oxidation of PVC-coated membrane material was performed using two testmethods of artificial accelerated weathering and outdoor weathering under different tensilestresses (0%,5%,10%and20%of the breaking strength). Yellowness index and tensile propertieswere tested under tensile stress during the experiments, so that we can have a whole understandingfor the performance of samples during the aging process. In addition, surface morphology andFourier transform infrared spectrometry (FTIR) was used to analyze the degradation products ofthe PVC-coated membrane material. The correlation between accelerated weathering and outdoorweathering under different tensile stresses was also studied during the experiment.The results showed that with the increase of aging time, the yellowness index increased andthe whiteness decreased. And the bigger the tensile stress was, the more the yellowness indexincreased and the whiteness decreased, namely the aging degree was more bigger. Also, the SEMshowed that the cracking phenomenon of the PVC coating was more and more obvious. When theweathering time was up to1000hours in the condition of artificial accelerated weathering, thesurface of PVC coating under tensile stress had the peeling phenomenon. It showed that the tensilestress promoted the cracking of the surface coating. While the surface color and surface propertieschanged significantly under tensile stress, the tensile properties did not change significantly. Itillustrated that the photo-oxidation of the PVC-coated membrane material initially happened onthe PVC-coating, and then on the fabric.Based on the aging results between the artificial accelerated weathering and outdoorweathering, the aging correlation analys is of PVC-Coated membrane material was obtained. Theresults showed that the change of the tensile strength retention, the tensile elongation retention andthe carbonyl index under two aging forms was consistent and the aging degree of the samples wasthe same, but when the cumulative UV radiation energy was the same, the performance existedsome difference. So it did not conform the reciprocity law. However, the change of the whiteness had an obvious difference. Therefore, the Schwarzschild’s law is valid when introducing a constant p on the basis of the reciprocity law. Its new form is:I t=constant That is, when the product of the p-th power of UV intensity and the aging time is the same, the photo-oxidation effects of the PVC-coated material are equivalent. It was found that, when p=0.87, the correlation of the samples between the artificial accelerated weathering and outdoor weathering is good. Then the whiteness under two aging forms is fitted according to the Schwarzschild’s law. The equations of the whiteness, the UV intensity and the aging time are obtained under20%stress. It is as follows: y=78.23-0.23x Where, x=I0.87t, I is the UV radiation intens ity and t is the aging time.The above equation showed that the relationships between the whiteness and the UV intensity, the aging time after fitted. It was seen from the equation that,when p=0.87, the artificial accelerated weathering and outdoor weathering had a good correlation. |
PDF Full Text Request