DEGRADATION OF URETHANE-FOAM-BACKED POLY(VINYL CHLORIDE) STUDIED USING RAMAN AND FLUORESCENCE MICROSCOPY

Urethane-foam-backed poly(vinyl chloride) (PVC) degrades through dehyd rochlorination, a process that results in the formation of conjugated polyene sequences within the backbone of the polymer. Raman spectrosco py at 633 nm and a combination of fluorescence spectroscopy and micros copy with blue excitation have been used to quantify the temporal degr adation of two commercial foam/vinyl composites. Since the resonance b ehavior of polyenes depends on their conjugation lengths, the Raman an d fluorescence measurements were most sensitive to polyenes with conju gation lengths of greater than or similar to 20 and similar to 10, res pectively, Durability tests were performed by weathering samples in th e field for 35 months and in ovens at temperatures of 100 and 120 degr ees C for similar to 500 h. For the field-weathered samples, the integ rated fluorescence intensity correlates well with the polyene concentr ation as determined by Raman measurements, which suggests that for the se aging conditions the kinetics controlling the steady-state populati ons of short- and long-length polyene sequences are similar. The resul ts from the laboratory-weathered samples are consistent with the concl usion that short-conjugation-length polyenes form first and then propa gate to longer conjugation lengths as degradation progresses. Most imp ortantly, this work demonstrates that the relatively simpler fluoresce nce imaging techniques fan be extremely useful in determining the comp arative weatherability of different foam/vinyl composites.