Aging properties of polyurethane elastomers under different environmental conditions
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摘要: 聚氨酯(Polyurethane，PU)具有出色的力学性能、耐热性、优良的抗冲击和抗疲劳特性，在航空航天、汽车等领域都有着广泛的应用，但是PU在实际应用中容易受到紫外光照、水分和化学介质的影响，导致物理和化学性能下降。为研究不同的环境对PU的老化作用及其对力学性能的影响，以聚四氢呋喃醚二醇(PTMEG)-2,4-甲苯二异氰酸酯(TDI)-2,4-二氨基-3,5-二甲硫基甲苯(DMTDA)为研究对象，通过测试PU不同环境条件下(高温—70℃和100℃、水浸、湿热—99℃等离子水、油浸—航空煤油、紫外)老化前后的性能变化，并利用FTIR来分析老化前后PU的化学结构变化。结果表明：PU在室温下浸泡168小时后的饱和吸湿率为1.8%。与未处理PU对比，PU在70℃和100℃下的环境中拉伸强度和硬度下降，撕裂强度增加；PU经过水浸处理后的拉伸强度和撕裂强度分别下降了6%和3%，硬度下降了4.2 HD；但是PU在湿热老化后拉伸强度和撕裂强度分别降低38.5%和32.9%，硬度降低22.7 HD；经过航空煤油浸泡后PU的拉伸强度和撕裂强度分别降低了13%和3%，硬度降低3.4 HD；PU经过紫外老化的拉伸强度和撕裂强度分别下降了38.6%和7%，硬度增加4.57 HD。FTIR结果表明，高温环境会使PU的醚键发生热氧老化；湿热环境使PU的氨基甲酸酯和脲基水解；紫外环境引发PU产生Photo-Fries重排反应。这些变化表明，PU易受紫外辐射和氧化影响。Abstract: Polyurethane (PU) boasts outstanding mechanical characteristics, such as robust heat resistance, exceptional impact resilience, and superior fatigue endurance, making it an extensively utilized material in the aerospace and automotive industries, among others. Despite these attributes, PU's practical performance can be compromised by exposure to ultraviolet radiation, moisture, and various chemical agents, which can lead to a deterioration of its physical and chemical properties. In order to investigate the aging effects of various environments on polyurethane (PU) and their impact on mechanical properties, polytetrahydrofuran ether diol (PTMEG)-2,4-toluene diisocyanate (TDI)-2,4-diamino-3,5-dimethylthiophenyl toluene (DMTDA) is selected as the research subject. The study involves measuring the moisture absorption of PU and assessing the changes in its mechanical properties before and after aging under different environmental conditions, such as high temperature(70℃ and 100℃), water immersion, humidity (99℃ ionized water), oil immersion(aviation kerosene), and UV. Furthermore, FTIR analysis is employed to analyze the chemical structural changes of PU before and after aging. This research aims to understand the aging effects of different environments on polyurethane (PU) and their influence on mechanical properties. The results show that the saturation moisture absorption rate of PU after being soaked at room temperature for 168 hours is 1.8%. Compared to the initial PU, the tensile strength and hardness of PU decrease in environments at 70℃ and 100℃, but the tear strength increases. After water immersion treatment, the tensile strength and tear strength of PU decrease by 6% and 3%, respectively, and the hardness decreases by 4.2 HD. However, after humid heat aging, the tensile strength and tear strength of PU decrease by 38.5% and 32.9%, respectively, and the hardness decreases by 22.7 HD. After immersion in aviation kerosene, the tensile strength and tear strength of PU decrease by 13% and 3%, respectively, and the hardness decreases by 3.4 HD. After UV aging, the tensile strength and tear strength of PU decrease by 38.6% and 7%, respectively, and the hardness increases by 4.57 HD. FTIR results indicate that high-temperature environments cause thermal oxidation aging of the ether bonds in PU; humid heat environments cause hydrolysis of the urethane and urea groups in PU; UV environments induce Photo-Fries rearrangement reactions in PU. These changes suggest that PU is susceptible to UV radiation and oxidation.
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Key words:
- Polyurethane /
- Mechanical properties /
- high temperature /
- Ultraviolet /
- Hygrothermal /
- Water absorption rate
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图 1 聚氨酯(PU)的主要原材料的结构式、化学反应式和微观结构
Figure 1. Structural formula, chemical reaction and microstructure of polyurethane (PU) main raw materials
图 2 (a)撕裂试样尺寸图和(b)拉伸试样尺寸图
Figure 2. (a) tear specimen size diagram and (b) tensile specimen size diagram
图 3 PU吸湿曲线及Fickian拟合结果
Figure 3. Comparison of water absorption curves and Fickian fitting results of polyurethane elastomers
图 4 PU经不同环境处理后的拉伸性能：(a)拉伸强度；(b)断裂伸长率；(c)拉伸载荷-位移曲线
Figure 4. Tensile properties of polyurethane elastomers after different environmental treatment: (a) tensile strength; (b) elongation at break;(c) tensile load-displacement curve
图 5 不同环境处理后PU的撕裂性能：(a)撕裂强度；(b)载荷-位移曲线
Figure 5. The tearing properties of polyurethane elastomers after different environmental treatment: (a) tear strength; (b) load-displacement curve
图 7 不同老化环境后聚氨酯弹性体的FTIR
Figure 7. Infrared spectra of polyurethane elastomers under different aging conditions
图 6 不同环境下PU的硬度
Figure 6. Hardness of polyurethane elastomers in different environmental
图 8 在高温下PU的FTIR中的亚甲基—CH2—变化
Figure 8. Change of methylene CH2 in FTIR of polyurethane elastomers at high temperature
图 10 吸湿后PU的FTIR的变化
Figure 10. Changes of FTIR of polyurethane elastomers after hygroscopicity
图 12 航空煤油处理后PU的FTIR的变化
Figure 12. Changes of FTIR of polyurethane elastomers after aviation kerosene treatment
图 13 紫外光照后PU的FTIR的变化
Figure 13. Change of FTIR of polyurethane elastomers after ultraviolet irradiation
图 14 Photo-Fries反应与醌酰亚胺的生成
Figure 14. Photo-Fries reaction and the formation of quinone imides
表 1 聚氨酯弹性体吸水性能参数
Table 1. Water absorption performance parameters of polyurethane elastomers
Sample Testing environment $ K $ $ h/{\mathrm{mm}} $ $ {M_{\mathrm{m}}}/\% $ $ D $ PU room temperature、168 h 0.286 2 1.832 0.01884 Notes: $ K $—Slope of the linear part of the water absorption curve of PU at room temperature; $ h $—Thickness of sample; $ {M_{\mathrm{m}}} $—Saturation moisture absorption rate of PU; $ D $—Diffusion coefficient of PU 
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