| Polymeric materials which have low density and excellent performance are being increasingly used in various applications.As one of the most useful commercial types of polymeric materials,thermoplastic polyurethane elastomers(TPU)which combine elastomeric properties and thermoplastic process are widely used in industry and consumer products,such as coatings,adhesives,films,shoe soles,automotive interior,biomaterials,etc.Particularly,the durability of polymeric materials is obviously affected by their service conditions such as sunlight,water,temperature,mechanical stress,etc.Hence,the research on the aging of polymeric materials has the academic and practical significance.Up to now,the common points that there were harmful effects on the physical and mechanical properties of the aged materials in the reported literatures of TPU aging.To the author's knowledge,few literatures dealing with the study of the TPU aging mechanism were published.In this thesis,aging behaviors,aging mechanisms and anti-aging methods of TPU were investigated via aging tests,such as UV-aging,thermo-oxidative aging,microwave aging,natural aging.Fourier transform infrared spectroscopy(FT-IR),proton nuclear magnetic resonance spectra(1H-NMR),and ultraviolet and visible absorption spectroscopy(UV-Vis)were used to characterize structural changes in TPU caused by photo and thermo-oxidative reactions.Firstly,we focus on studying the aging mechanisms of TPU.(1)There were no structural changes of TPU caused by UV irradiation,except that the concentration of hydrogen-bonded urethane carbonyl groups had a tendency to higher values with increasing irradiation time.What's more,formation of the enamine led to the yellowing of TPU.(2)It was found that TPU exposed to microwave and thermal oxidative had the same aging mechanism.TPU had a post-curing at first,then isocyanurate groups reacted with the primary amine to form the carbamido,further reacted to form biuret groups and to degrade.In the presence of microwave for 30 minutes or thermo-oxidative condition for 50 hours at 190?,the absorption to microwave or heat induced degradation of TPU and formation of poly(butylene adipate)(PBA).Therefore,microwave aging was more efficient than thermo-oxidative aging,caused by the difference of internal heating and external heating.(3)Due to the complexity of natural environment,both the mechanism of UV-aging and the mechanism of thermo-oxidative aging existed in the natural aging of TPU.It was mainly UV-aging at first,and then thermo-oxidative aging started after 1 year later.And the durability of TPU was closely related to its hard segment content.In UV-aging,thermo-oxidative aging,and natural aging,TPU 1190A had better stability than TPU 1180A.More importantly,a linear relationship between artificial UV-aging and natural aging was builded for the first time.It was found that UV-aging for 1 hour was same to natural aging for 460 hours(1180A).365 hours(1190A),and thermo-oxidative aging for 5 hours at 190 ? was similar to natural aging for 12 months.Furthermore,it provided the important theoretical basis for study of TPU aging and estimation of TPU service life.Then,we used UV-531?BHT?and antioxidant 1076 to improve the durability of TPU.The follows were what we had found:There were same changes when the TPU which UV-531 was 0.3%by weight exposed to UV irradiation for 4 hours or the TPU that had no additive aged for 2 hours under UV radiation;The aging behaviors of the TPU which antioxidants were 0.7%by weight under thermo-oxidative aging for 25 hours at 190? were similar to the thermo-oxidative aging of the TPU that had no additive for 15 hours.What's more,the combination of UV-531 and BHT or UV-531 and antioxidant 1076 had a positive synergistic effect on the photo stabilization of TPU.While,there was no positive synergistic effect on the heat stabilization of TPU. |
PDF Full Text Request