Photodegradation of cellulose acetate fibers

Abstract

The photodegradation of cellulose acetate fibers by ultraviolet light in vacuo at 77°K and at ambient temperature was studied. Three kinds of light sources with different wavelengths between 2353 and 6000 Å were employed. ESR studies at 77°K show that several kinds of free radicals are produced from cellulose diacetate (CDA) and cellulose triacetate (CTA) fibers when irradiated with light of wavelength shorter than 2800 Å. Among these methyl radicals formed decayed within 210 min at 77°K. When the temperature was raised above 77°K, radical transformation occurred at 87°K and most of the free radicals decayed at 193°K, whereas the cellulosic radicals were stable at this and even at higher temperatures. Ultraviolet spectroscopy studies revealed that the main chromophores are the carbonyl function of the acetyl group and acetal groups in the polymer. The photodegradation of the polymers at ambient temperature resulted in the formation of gaseous products (mainly CO, CO2, and CH4), together with the loss of bound acetic acid content and sample weight. Decreases in viscosity and reduction of tensile strength and elongation were also observed in the irradiated samples, revealing that the overt effects of ultraviolet light on cellulose acetate fibers are interpreted in terms of free‐radical reactions ultimately leading to main‐chain and side‐group scissions, unsaturation, and the formation of small molecule fragments. Among these, main‐chain scission took place predominantly in CDA fiber and side‐group scission in CTA fiber. The mechanism of the fundamental photochemical degradation processes of cellulose acetate fibers is elucidated.

Photodegradation of cellulose acetate film in the presence of benzophenone as a photosensitizer

“…CA films were placed in glass vials (20 mL, 23 Â 75 mm 2 ) and the vials were sealed with aluminum caps attached by poly(tetrafluoroethylene)/silicon septum, and then they were exposed to light from a xenon arc lamp of 1.5 kW in a fadometer TS-2 (Suga Test Instruments, Tokyo, Japan). The light was filtered at the cut-off value of 275 nm so that the spectra were similar to those from the solar according to the spectra data in the user's manual of the fadometer.…”

“…[1][2][3] Hon has reported that ultraviolet exposure to CA fibers led to loss of sample weight and acetic acid content. 2 In our previous study using a xenon fadometer for light stability tests, however, CA films showed no detectable acetic acid generation or decrease in the molecular weight by photoirradiation for at least 28 days. 4 Therefore, photodegradation of CA under ambient environment seems to be very slow.…”

Degradation of Cellulose Acetate-Based Materials: A Review

“…Cellulose acetate has an absorption at approximately 260 nm which is attributed to ketonic carbonyl groups [53]. In consideration of the fact, that the sunlight reaching earth's surface after being filtered by the atmosphere has a lower cut-off of approximately 300 nm, one might conclude that cellulose acetate does not significantly photo degrade in a natural environment.…”

“…The studies by Hon [53] provided insight into the mechanisms, which comprises both a polymer chain scission of the glucosidic bond and a cleavage of side groups. Acetate fibers were irradiated in quartz tubes within the ESR cavity under vacuum at 77 K with far UV-light.…”

“…Besides biological degradation, photo degradation is an important route for decomposing cellulose acetate Cellulose acetate is made from raw materials with a high content of a-cellulose, but still contains some impurities which might be responsible for the absorption of light in the far UV light region with wavelengths shorter than 280 nm range [52][53][54]. Cellulose acetate has an absorption at approximately 260 nm which is attributed to ketonic carbonyl groups [53].…”