Degradation of Urethane-Foam-Backed Poly(Vinyl Chloride) Studied Using Raman and Fluorescence Microscopy

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-conjugation-length 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.

Cross-linking of polytetrafluoroethylene during room-temperature irradiation

“…The increase in fluorescence intensity that is observed for the high dose samples is likely explained by production of conjugated double bond (C]C) species within the polymer during irradiation, as discussed in a previous study [18]. Presence of conjugated double-bond moieties resulting in polymer fluorescence has also been observed during the thermal degradation of other polymers [20][21][22][23][24]. Further evidence for the existence of C]C species is observed in the FTIR analysis of a-irradiated PTFE samples, and is discussed below.…”

“…7, which displays FTIR spectra in the 1050-675 cm À1 region for a variety of samples. The bottom spectrum is that for virgin PTFE and represents the features expected in this region for undamaged PTFE, while the top spectrum is obtained from the 4th layer of a stacked PTFE sample (15)(16)(17)(18)(19)(20) mm depth) exposed to 10 8 Gy of a-radiation representing heavily radiation-damaged material. The four spectra in the middle are obtained from the 7th layers (representing 30-35 mm depth into the sample) of stacked PTFE samples exposed to 10 5 -10 8 Gy of a-radiation.…”

Depth Profiling of the Optical Absorption Coefficient in Ultraviolet-Degraded Poly(Vinylchloride) Films by Dual Beam Light Profile Microscopy

“…This dependence often derives from restrictions on the transport of reagents to within short distances from a surface or interface in a material. A classic effect is the yellowing of many polymers [2][3][4][5][6][7][8][9][10][11][12][13] under exposure to UV radiation. This process occurs efficiently in zones of a material in which oxygen concentrations are low or negligible, at depths of tens or hundreds of micrometers below the surface.…”

“…In poly(vinyl chloride) (PVC) [2][3][4][5][6][7][8][9] and related polymers such as poly(vinyl alcohol) (PVA) [10][11][12] and poly(vinyl acetate) (PVAc), 13 when thin films are subjected to thermal or UV photo-degradation, yellowing arises from the for-mation of poly(ene) chains of structure -(CHϭCH) n -. As degradation proceeds, the chain length n increases from 2-4 through 12 units or greater, 7,12 producing increased visible wavelength absorption in sub-surface zones.…”

Formation of optical color and fluorescence centers in polytetrafluoroethylene under γ-irradiation

“…A feature of these polymers was the fact that their main molecular chain consisted of C atoms. Such polymers include polystyrene [11][12][13], polyvinyl alcohol [14], polyvinylchloride [15], and several others. A similar hypothesis about the structure of the fluorescence centers of PTFE irradiated by α-particles (10 7 -10 8 Gy dose) was made [8].…”