Study On CeO₂/TPU Sub-microstructure Control And UV Aging Resistance Modification

Thermoplastic polyurethane elastomers(TPU)are widely used in power cables,automotive interiors and medical devices due to its excellent properties.However,the poor UV aging resistance of TPU limits it being applied in more applications.Inorganic nanoparticles which can absorb UV light can be used to improve the UV aging resistance of TPU.Nano cerium oxide(CeO2)has high UV absorption efficiency and can be used to improve the UV aging resistance of TPU.The Ce3+/Ce4+conversion caused by oxygen defect structure of CeO2 can eliminate the free radicals produced by TPU during UV aging and inhibit the molecular chain breaking.It is necessary to modify the CeO2 to improve its dispersion in the TPU matrix.The combination of CeO2 and organic UV aging additives can improve the UV absorption efficiency.The UV aging resistance of TPU can be improved under the synergistic effect of the CeO2 and organic UV aging additives.Therefore,CeO2 of two sizes were filled with TPU by two mixing methods to study the effect on the structure and properties of TPU in this paper.Then,CeO2 was modified to improve the interface binding ability with TPU and the dispersion in TPU.Finally,TPU was filled with CeO2 and UV-327 to study the effect of the synergistic effect of CeO2 and UV-327 on the UV aging resistance of TPU.The details are as follows:(1)TPU was synthesized by hexamethylene diisocyanate(HDI):polytetrahydrofuran(PTMG):1,4-butanediol(1,4-BD)in the molar ratio of 3:2:1.CeO2 of two sizes were added before TPU prepolymerization(premixing method)or after chain extension(blending method).The result shows that hybrid methods have a greater influence than the size of CeO2 on the microstructure and properties of TPU.Because CeO2 is added before prepolymerization by premixing method,the structure of soft and hard segments is disordered during the reaction.The distance between the molecular chains increases,and it is difficult to form an orderly arrangement of soft and hard segments.Because CeO2 is added after TPU synthesis reaction by blending method,the molecular structure of TPU has been formed,so it has little influence on the structure of TPU.CeO2 has better dispersibility in TPU composites prepared by premixing method due to longer dispersion time,The tensile mechanical properties and thermal stability of TPU composites prepared by premixing method are better.The tensile strength and elongation at break are 11.6 MPa and 1492%respectively.The decomposition temperature TG50%is 23.4℃ higher than pure TPU.2)Firstly,CeO2 was modified by polyacrylic acid(PAA).Amino groups were modified on the surface of CeO2(CeO2-EDA)by the reaction of ethylenediamine(EDA)with PAA.TPU was synthesized by diphenylmethane diisocyanate(MDI)polycaprolactone glycol(PCL):1,4-BD in the molar ratio of 3.05:2:1.CeO2 and CeO2-EDA were added after chain extension.FT-IR and HRTEM results show that CeO2-EDA reacted with isocyanate terminated prepolymer.The results show that the interface bonding ability of CeO2 and TPU is improved,and the dispersibility of CeO2 in TPU matrix is better.The tensile mechanical properties and thermal stability of TPU filled with CeO2-EDA are better.The maximum tensile strength is 48.2 MPa.The thermal degradation temperature TG10%and TG50%are increased by 14.0 and 7.4℃ respectively CeO2 and CeO2-EDA have strong UV absorption.After UV aging,the tensile strength retention rate of TPU filled with 3%CeO2-EDA increased from 69.2%to 90.7%compared with pure TPU3)CeO2(m-CeO2)was modified by titanatec oupling agent NDZ-201.TPU was filled by m-CeO2 and UV-327.The results show that after 60 days of UV aging,the breaking strength of TPU,TPU with 0.5%m-CeO2,TPU with 0.5%m-CeO2 and 0.5%UV-327 and TPU with 0.5%m-CeO2 and 1%UV-327 decreased to 25.4%,34.9%,61.8%and 71.3%of that before aging,respectively.The results of SEM show that cracks and bulges appear on the surface of TPU after 60 days of UV aging.It is possible that the Photo-Fries rearrangement of TPU or the generation of free radicals lead to the molecular chain breaking during UV aging.The morphology of TPU filled modified with m-CeO2 and UV-327 do not change significantly.UV-327 and m-CeO2 have different anti-ultraviolet aging mechanisms.The combination of m-CeO2 and UV-327 can improve the UV absorption efficiency and the UV aging resistance of TPU.