Wiggins Michael J, Anderson James M, Hiltner Anne
Center for Applied Polymer Research and Department of Macrocellular Science, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, USA.
J Biomed Mater Res A. 2003 Sep 1;66(3):463-75. doi: 10.1002/jbm.a.10584.
A diaphragm-type film specimen was used to study in vitro degradation of poly(etherurethane urea) (PEUU) under conditions of dynamic loading. This geometry allowed both uniaxial and biaxial loading in a single experiment. During testing, the film was exposed to a H(2)O(2)/CoCl(2) solution that simulated in vivo oxidation of PEUU. The combination of dynamic loading and biaxial tensile strain accelerated oxidative degradation. The effects of biaxial strain magnitude and strain rate were examined separately by increasing the frequency of fatigue loading from 0 to 1 Hz with constant maximum biaxial strain and by changing the maximum biaxial strain while maintaining constant strain rate. In the ranges of biaxial strain energy (0.17 to 0.55 MPa) and strain rate (0 to 46% s(-1)) tested, the rate of degradation increased with increasing strain rate whereas strain magnitude had essentially no effect on degradation rate. Although loading conditions affected the rate of oxidative degradation, ATR-FTIR analysis suggested that in all cases the mechanism of degradation did not change. Chemical degradation produced a brittle crosslinked surface layer marked by dimpling and pitting, as observed with scanning electron microscopy. Pits served as stress concentrators and initiated environmental stress cracks under dynamic loading but not under static (creep) loading. Small pits were sufficient to initiate cracks at higher strain rates whereas only large pits initiated cracks at lower strain rates. Consequently, a higher strain rate produced more profuse cracking.
使用隔膜式薄膜试样研究聚（醚聚氨酯脲）（PEUU）在动态加载条件下的体外降解。这种几何形状允许在单个实验中进行单轴和双轴加载。在测试过程中，薄膜暴露于模拟PEUU体内氧化的H₂O₂/CoCl₂溶液中。动态加载和双轴拉伸应变的组合加速了氧化降解。通过在恒定的最大双轴应变下将疲劳加载频率从0增加到1 Hz以及在保持恒定应变率的同时改变最大双轴应变，分别研究了双轴应变幅度和应变率的影响。在所测试的双轴应变能（0.17至0.55 MPa）和应变率（0至46% s⁻¹）范围内，降解速率随应变率的增加而增加，而应变幅度对降解速率基本没有影响。尽管加载条件影响氧化降解速率，但ATR-FTIR分析表明，在所有情况下降解机制都没有改变。化学降解产生了一个脆性的交联表面层，其特征是出现凹坑和麻点，如扫描电子显微镜观察到的那样。凹坑作为应力集中器，在动态加载下引发环境应力裂纹，但在静态（蠕变）加载下不会引发。小凹坑足以在较高应变率下引发裂纹，而只有大凹坑在较低应变率下引发裂纹。因此，较高的应变率会产生更大量的裂纹。
