ABSTRACT:The degradation behavior of an elastomeric polyurethane (PU) was investigated with accelerated ultraviolet (UV) and hygrothermal (HT) techniques. Samples were subjected to UV exposure and HT conditions for 3 or 5 months and were removed in 1-month intervals from the test chambers. Their chemical structure was evaluated with Fourier transform infrared (FTIR) spectroscopy. The thermal transitions of the aged samples were evaluated with differential scanning calorimetry (DSC). Both FTIR and DSC results showed no evidence of significant structural damage to the HT-aged PU throughout exposure. FTIR analysis of the UV-aged samples showed a noticeable change in the chemical structure of the polymer after 1 month of UV exposure. The results from DSC correlated with the FTIR analysis of the UV-aged samples. Spectroscopic and thermal analysis of the aging of the PU samples was correlated to mechanical analysis.

In this study, the effects of environmental aging on the mechanical performance of elastomeric polyurethane (PU) were investigated using two accelerated aging techniques, namely, ultraviolet (UV) and hygrothermal (HT). Samples were prepared and subjected to UV and HT exposure for a period of 5 months and removed and mechanically tested at different time intervals. Differential scanning calorimetry (DSC) was performed. A noticeable change in the chemical structure of the PU after 1 month of UV exposure was found, however, that was not the case after 1 month of HT exposure. The stress and strain to failure, tearing energy, and storage modulus were evaluated at different intervals for both aging techniques.It was found that the UV exposure caused severe degradation of the PU in comparison with the HT. A reduction of more than 98% in the tearing energy was observed for the UV-exposed samples after 5 months when compared with only a 35% reduction in the tearing energy for the HTexposed samples. A similar trend was observed for tear strength and storage modulus. The degradation mechanisms of the PU elastomers have been identified using SEM and correlated with the tearing energy.

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Nanocomposites using EPON 824 as their matrix were exposed to pulse laser at 532 nm for various time intervals. The developed nanomaterials used for this study were manufactured using EPON 824 with multiwalled carbon nanotubes (MWCNTs) at a loading rate of 0.15% by weight and nanoclays at a loading rate of 2% by weight as reinforcements. The effect of laser irradiation on polymer composites has been investigated. The degradation mechanism for the epoxy was of a laser induced burning nature. Of all specimens tested, the ultimate strength of the MWCNT-reinforced specimens decreased the most as a function of radiation time; the nanoclay-reinforced epoxy retained the most strength after 2 min of laser radiation. In addition, the threshold fluence for decomposition indicated that less energy was required to initiate decomposition in the MWCNT-reinforced epoxy than in the nanoclay-reinforced epoxy. This can be attributed to the high thermal conductivity of the carbon nanotubes. Measurement of surface damage in the material was observed via electron microscopy. Fourier transform infrared spectroscopy was used to investigate changes to the molecular structure as a function of exposure time.

A poly(vinyl chloride/vinyl acetate) copolymer (VYHH) with and without multiwalled carbon nanotubes (MWCNTs) as reinforcements were used as a coating for steel substrates to evaluate their barrier properties against corrosion. Electrical impedance and thermal properties of the coatings were evaluated. The coatings were formulated with 0.1% MWCNT, by weight. Neat and nano-filled VYHH was used to coat polished, degreased steel substrates via a dipping method. The substrates were either dipped once, for a target coating thickness of 30-40 lm, or twice for a target coating thickness of 60-75 lm. The coated and uncoated control samples were submerged in a tank with a 5% NaCl solution for a 45-day period. Electrochemical impedance spectroscopy (EIS) revealed that coating thickness plays a role in corrosion resistance.EIS also showed that nano-reinforced VYHH had the highest charge transfer resistance within its coating thickness. Fourier transform infrared spectroscopy (FTIR) indicated that hydrolysis occurred in the single coatings for both the neat and nanoreinforced coatings. Differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA) both showed that the addition of MWCNTs improved the thermal stability of the VYHH. DSC thermograms revealed that the thermal properties of the nano VYHH were largely unchanged after 45 days of submersion as compared with the unaged nano VYHH. V V C 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: [15][16][17][18][19][20][21][22] 2011