Abstract
Urethane-foam-backed poly(vinyl chloride) (PVC) degrades through dehydrochlorination, a process that results in the formation of conjugated polyene sequences within the backbone of the polymer. Raman spectroscopy at 633 nm and a combination of fluorescence spectroscopy and microscopy with blue excitation have been used to quantify the temporal degradation of two commercial foam/ vinyl composites. Since the resonance behavior of polyenes depends on their conjugation lengths, the Raman and fluorescence measurements were most sensitive to polyenes with conjugation lengths of > 20 and ~ 10, respectively. Durability tests were performed by weathering samples in the field for 35 months and in ovens at temperatures of 100 and 120 C for ~ 500 h. For the field-weathered samples, the integrated fluorescence intensity correlates well with the polyene concentration as determined by Raman measurements, which suggests that for these aging conditions the kinetics controlling the steady-state populations of short- and long-length polyene sequences are similar. The results from the laboratory-weathered samples are consistent with the conclusion that short-conjugationlength polyenes form first and then propagate to longer conjugation lengths as degradation progresses. Most importantly, this work demonstrates that the relatively simpler fluorescence imaging techniques can be extremely useful in determining the comparative weatherability of different foam/vinyl composites.
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