{'fraction_non_alphanumeric': 0.03319838056680162, 'fraction_numerical': 0.027530364372469637, 'mean_word_length': 5.4375, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Accelerated Hygrothermal and UV Aging of Thermoplastic Polyurethanes

Thermoplastic polyurethanes (PU) were prepared from 4,4'-diphenyl methane diisocyanate (MDI), polyether polyol and 1,4 butane diol with and without a hindered amine light stabilizer (Tinuvin®-123) and UV absorber (Tinuvin®-400). The accelerated hygrothermal and UV aging were performed at different humidity and aging temperatures for 720, 1440, and 2160 h of exposure, in a Thermotron environmental chamber and QUV chamber, respectively. Fourier transform infrared spectroscopy was used to evaluate the structural changes during aging. The thermal transition for PU, studied by differential scanning calorimetry showed a marginal structural damage after hygrothermal aging. After only 720 h of UV exposure, the neat PU showed a noticeable change in the chemical structure; however, the stabilized one showed almost no change. Tensile strength for the neat PU deteriorated by about 47% after 2160 h of UV exposure; however, the stabilized polyurethane maintained its almost original strength (i.e., 83% retention) after the whole exposure time. The acceleration factor was found to be 6 and the predicted life time for the stabilized polyurethane was about 6 years.